Sample records for supernova dark energy

A decade ago the observations of thermonuclear supernovae at high-redhifts showed that the expansion rate of the Universe is accelerating and since then, the evidence for cosmic acceleration has gotten stronger. This acceleration requires that the Universe is dominated by darkenergy, an exotic component characterized by its negative pressure. Nowadays all the available astronomical data (i.e. thermonuclear supernovae, cosmic microwave background, barionic acoustic oscillations, large scale structure, etc.) agree that our Universe is made of about 70% of darkenergy, 25% of cold dark matter and only 5% of known, familiar matter. This Universe is geometrically flat, older than previously thought, its destiny is no longer linked to its geometry but to darkenergy, and we ignore about 95% of its components. To understand the nature of darkenergy is probably the most fundamental problem in physics today. Current astronomical observations are compatible with darkenergy being the vacuum energy. Supernovae have played a fundamental role in modern Cosmology and it is expected that they will contribute to unveil the darkenergy. In order to do that it is mandatory to understand the limits of supernovae as cosmological distance indicators, improving their precision by a factor 10.

Nowadays it is widely accepted that the current Universe is dominated by darkenergy and exotic matter, the so called StandardModel of Cosmoloy or CDM model. All the available data (Thermonuclear Supernovae, Cosmic Microwave Background, Baryon Acoustic Oscillations, Large Scale Structure, etc.) are compatible with a flat Universe made by ~70% of darkenergy. Up to now observations agree that darkenergy may be the vacuum energy (or cosmological constant) although improvements are needed to constrain further its equation of state. In this context, the cosmic destiny of the Universe is no longer linked to its geometry but to the nature of darkenergy; it may be flat and expand forever or collapse. To understand the nature of darkenergy is probably the most fundamental problem in physics today; it may open new roads of knowledge and led to unify gravity with the other fundamental interactions in nature. It is expected that astronomical data will continue to provide directions to theorists and experimental physicists. Type Ia supernovae (SNe Ia) have played a fundamental role, showing the acceleration of the expansion rate of the Universe a decade ago, and up to now they are the only astronomical observations that provide a direct evidence of the acceleration. However, in order to determine the source of the darkenergy term it is mandatory to improve the precision of supernovae as distance indicators on cosmological scale.

Type Ia supernovae are a powerful cosmological probe, that gave the first strong evidence that the expansion of the universe is accelerating. Here we provide an overview of how supernovae can go further to reveal information about what is causing the acceleration, be it darkenergy or some modification to our laws of gravity. We first summarise the many different approaches used to explain or test the acceleration, including parametric models (like the standard model, LambdaCDM), non-parametric models, dark fluid models such as quintessence, and extensions to standard gravity. We also show how supernova data can be used beyond the Hubble diagram, to give information on gravitational lensing and peculiar velocities that can be used to distinguish between models that predict the same expansion history. Finally, we review the methods of statistical inference that are commonly used, making a point of separating parameter estimation from model selection.

Based on an analysis of 42 high-redshift supernovae discovered by the supernovae cosmology project, we have found evidence for a positive cosmological constant, Lambda, and hence an accelerating universe. In particular, the data are strongly inconsistent with a Lambda=0 flat cosmology, the simplest inflationary universe model. The size of our supernova sample allows us to perform a variety of statistical tests to check for possible systematic errors and biases. We will discuss results of these and other studies and the ongoing hunt for further loopholes to evade the apparent consequences of the measurements. We will present further work that begins to constrain the alternative physics theories of "darkenergy" that have been proposed to explain these results. Finally, we propose a new concept for a definitive supernova measurement of the cosmological parameters.

The Supernova Acceleration Probe (SNAP) will use Type Ia supernovae (SNe Ia) as distance indicators to measure the effect of darkenergy on the expansion history of the Universe. (SNAP's weak-lensing program is described in a companion White Paper.) The experiment exploits supernova distance measurements up to their fundamental systematic limit; strict requirements on the monitoring of each supernova's properties lead to the need for a space-based mission. Results from pre-SNAP experiments, which characterize fundamental SN Ia properties, will be used to optimize the SNAP observing strategy to yield data, which minimize both systematic and statistical uncertainties. SNAP has achieved technological readiness and the collaboration is poised to begin construction.

A model-independent method to study the possible evolution of darkenergy is presented. Optimal estimates of the darkenergy equation of state w are obtained from current supernovae data from Riess et al. (2004) following a principal components approach. We assess the impact of varying the number of piecewise constant estimates of w using a model selection method, the Bayesian information criterion, and compare the most favored models with some parametrizations commonly used in the literature. Although data seem to prefer a cosmological constant, some models are only moderately disfavored by our selection criterion: a constant w, w linear in the scale factor, w linear in redshift and the two-parameter models introduced here. Among these, the models we find by optimization are slightly preferred. However, current data do not allow us to draw a conclusion on the possible evolution of darkenergy. Interestingly, the best fits for all varying-w models exhibit a w

Understanding the origin of the accelerated expansion of the Universe poses one of the greatest challenges in physics today. Lacking a compelling fundamental theory to test, observational efforts are targeted at a better characterization of the underlying cause. If a new form of mass-energy, darkenergy, is driving the acceleration, the redshift evolution of the equation of state parameter w(z) will hold essential clues as to its origin. To best exploit data from observations it is necessary to develop a robust and accurate reconstruction approach, with controlled errors, for w(z). We introduce a new, nonparametric method for solving the associated statistical inverse problem based on Gaussian process modeling and Markov chain Monte Carlo sampling. Applying this method to recent supernova measurements, we reconstruct the continuous history of w out to redshift z=1.5.

We study the effect of filter zero-point uncertainties on future supernovadarkenergy missions. Fitting for calibration parameters using simultaneous analysis of all Type Ia supernova standard candles achieves a significant improvement over more traditional fit methods. This conclusion is robust under diverse experimental configurations (number of observed supernovae, maximum survey redshift, inclusion of additional systematics). This approach to supernova fitting considerably eases otherwise stringent mission cali- bration requirements. As an example we simulate a space-based mission based on the proposed JDEM satellite; however the method and conclusions are general and valid for any future supernovadarkenergy mission, ground or space-based.

Cosmological measurements suggest that our universe contains a darkenergy component. In order to study the darkenergy evolution, we constrain a parameterized darkenergy equation of state ω(z) = ω0+ω1(z/1+z) using the recent observational datasets: 157 Gold type la supernovae and the newly released 182 Gold type la supernovae by the maximum likelihood method. It is found that the best fit ω(z) crosses -1 in the past and the present best fit value of ω(0)＜-1 obtained from 157 Gold-type la supernovae. The crossing of -1 is not realized and ω0=-1 is not ruled out in 1σ confidence level for the 182 Gold-type la supernovae. It is also found that the range of parameter ω0 is wide even in 1σ confidence level and the best fit ω(z) is sensitive to the prior of Ωm.

The nature of darkenergy is a mystery to us. This paper uses the supernova data to explore the property of darkenergy by some model independent methods. We first Talyor expanded the scale factor $a(t)$ to find out the deceleration parameter $q_0<0$. This result just invokes the Robertson-Walker metric. Then we discuss several different parameterizations used in the literature. We find that $\\Omega_{\\rm DE0}$ is almost less than -1 at $1\\sigma$ level. We also find that the transition redshift from deceleration phase to acceleration phase is $z_{\\rm T}\\sim 0.3$.

The DarkEnergy Camera on the Blanco 4-m Telescope is an ideal instrument for identifying rapid optical transients with its large field of view and four optical filters. We utilize two seasons of data from the DarkEnergy Survey to search for kilonovae, an optical counterpart to gravitational waves from binary neutron star mergers. Kilonova lightcurves from Barnes and Kasen inform our analysis for removing background signals such as supernovae. We simulate DES observations of kilonovae with the SNANA software package to estimate our search efficiency and optimize cuts. Finally, we report rate limits for binary neutron star mergers and compare to existing rate estimates.

We present an analysis of supernova light curves simulated for the upcoming DarkEnergy Survey (DES) supernova search. The simulations employ a code suite that generates and fits realistic light curves in order to obtain distance modulus/redshift pairs that are passed to a cosmology fitter. We investigated several different survey strategies including field selection, supernova selection biases, and photometric redshift measurements. Using the results of this study, we chose a 30 square degree search area in the griz filter set. We forecast 1) that this survey will provide a homogeneous sample of up to 4000 Type Ia supernovae in the redshift range 0.05supernova with an identified host galaxy will be obtained from spectroscopic observations of the host. A supernova spectrum will be obtained for a subset of the sample, which will be utilized for control studi...

We present the results of a study of selection criteria to identify Type Ia supernovae photometrically in a simulated mixed sample of Type Ia supernovae and core collapse supernovae. The simulated sample is a mockup of the expected results of the DarkEnergy Survey. Fits to the MLCS2k2 and SALT2 Type Ia supernova models are compared and used to help separate the Type Ia supernovae from the core collapse sample. The DarkEnergy Task Force Figure of Merit (modified to include core collapse supernovae systematics) is used to discriminate among the various selection criteria. This study of varying selection cuts for Type Ia supernova candidates is the first to evaluate core collapse contamination using the Figure of Merit. Different factors that contribute to the Figure of Merit are detailed. With our analysis methods, both SALT2 and MLCS2k2 Figures of Merit improve with tighter selection cuts and higher purities, peaking at 98% purity.

Supernova experiments to characterize darkenergy require a well designed low redshift program; we consider this for both ongoing/near term (e.g. Supernova Legacy Survey) and comprehensive future (e.g. SNAP) experiments. The derived criteria are: a supernova sample centered near z=0.05 comprising 150-500 (in the former case) and 300-900 (in the latter case) well measured supernovae. Low redshift Type Ia supernovae play two important roles for cosmological use of the supernova distance-redshift relation: as an anchor for the Hubble diagram and as an indicator of possible systematics. An innate degeneracy in cosmological distances implies that 300 nearby supernovae nearly saturate their cosmological leverage for the first use, and their optimum central redshift is z=0.05. This conclusion is strengthened upon including velocity flow and magnitude offset systematics. Limiting cosmological parameter bias due to supernova population drift (evolution) systematics plausibly increases the requirement for the second us...

Final technical report for project "Type Ia Supernovae: Tools for the Study of DarkEnergy" awarded jointly to scientists at the University of California, Santa Cruz and Berkeley, for computer modeling, theory and data analysis relevant to the use of Type Ia supernovae as standard candles for cosmology.

Upcoming imaging surveys such as the Large Synoptic Survey Telescope will repeatedly scan large areas of sky and have the potential to yield million-supernova catalogs. Type Ia supernovae are excellent standard candles and will provide distance measures that suffice to detect mean pairwise velocities of their host galaxies. We show that when combining these distance measures with photometric redshifts for either the supernovae or their host galaxies, the mean pairwise velocities of the host galaxies will provide a darkenergy probe which is competitive with other widely discussed methods. Adding information from this test to type Ia supernova photometric luminosity distances from the same experiment, plus the cosmic microwave background power spectrum from the Planck satellite, improves the DarkEnergy Task Force Figure of Merit by a factor of 2.2. Pairwise velocity measurements require no additional observational effort beyond that required to perform the traditional supernova luminosity distance test, but m...

The present uncertainty in the value of the Hubble constant (resulting in an uncertainty in OmegaM) and the paucity of Type Ia supernovae at redshifts exceeding 1 are leading obstacles to determining the nature of darkenergy. We conducted a single, integrated set of observations in Cycle 15 to provide a 40% improvement in constraints on darkenergy. This program observed known Cepheids in six reliable hosts of Type Ia supernovae with NICMOS, to reduce the uncertainty in H0 by a factor of two because of the smaller dispersion along the instability strip, the diminished extinction, and the weaker metallicity dependence in the infrared. In parallel with ACS, at the same time the NICMOS observations were underway, we discovered and followed a sample of Type Ia supernovae at z > 1. Together, these measurements, along with prior constraints from WMAP, should provide a significant improvement in our ability to distinguish between a static, cosmological constant and dynamical darkenergy.

Supernova experiments to characterize darkenergy require a well designed low redshift program; we consider this for both ongoing/near term (e.g. Supernova Legacy Survey) and comprehensive future (e.g. SNAP) experiments. The derived criteria are: a supernova sample centered near z≈0.05 comprising 150 500 (in the former case) and 300 900 (in the latter case) well measured supernovae. Low redshift Type Ia supernovae play two important roles for cosmological use of the supernova distance-redshift relation: as an anchor for the Hubble diagram and as an indicator of possible systematics. An innate degeneracy in cosmological distances implies that 300 nearby supernovae nearly saturate their cosmological leverage for the first use, and their optimum central redshift is z≈0.05. This conclusion is strengthened upon including velocity flow and magnitude offset systematics. Limiting cosmological parameter bias due to supernova population drift (evolution) systematics plausibly increases the requirement for the second use to less than about 900 supernovae.

The final technical report from the project "Discovering the Nature of DarkEnergy: Towards Better Distances from Type Ia Supernovae" led at Rutgers the State University of New Jersey by Prof. Saurabh W. Jha is presented, including all publications resulting from this award.

The persisting consistency of ever more accurate observational data with the predictions of the standard LCDM cosmological model puts severe constraints on possible alternative scenarios, but still does not shed any light on the fundamental nature of the cosmic dark sector.As large deviations from a LCDM cosmology are ruled out by data, the path to detect possible features of alternative models goes necessarily through the definition of cosmological scenarios that leave almost unaffected the background and -- to a lesser extent -- the linear perturbations evolution of the universe. In this context,the Multi-coupled DE (McDE) model was proposed by Baldi 2012 as a particular realization of an interacting DarkEnergy field characterized by an effective screening mechanism capable of suppressing the effects of the coupling at the background and linear perturbation level. In the present paper, for the first time, we challenge the McDE scenario through a direct comparison with real data, in particular with the lumi...

The present uncertainty in the value of the Hubble constant {resulting in anuncertainty in Omega_M} and the paucity of Type Ia supernovae at redshiftsexceeding 1 are now the leading obstacles to determining the nature of darkenergy. We propose a single, integrated set of observations for Cycle 15 thatwill provide a 40% improvement in constraints on darkenergy. This programwill observe known Cepheids in six reliable hosts of Type Ia supernovae withNICMOS, reducing the uncertainty in H_0 by a factor of two because of thesmaller dispersion along the instability strip, the diminished extinction, andthe weaker metallicity dependence in the infrared. In parallel with ACS, atthe same time the NICMOS observations are underway, we will discover andfollow a sample of Type Ia supernovae at z > 1. Together, these measurements,along with prior constraints from WMAP, will provide a great improvement inHST's ability to distinguish between a static, cosmological constant anddynamical darkenergy. The Hubble Space Telescope is the only instrument inthe world that can make these IR measurements of Cepheids beyond the LocalGroup, and it is the only telescope in the world that can be used to find andfollow supernovae at z > 1. Our program exploits both of these uniquecapabilities of HST to learn more about one of the greatest mysteries inscience.

The Department of Energy (DOE) hosted an event Friday, January 13, with 2011 Physics Nobel Laureate Saul Perlmutter. Dr. Perlmutter, a physicist at the Department’s Lawrence Berkeley National Laboratory and a professor of physics at the University of California at Berkeley, won the 2011 Nobel Prize in Physics “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.” DOE’s Office of Science has supported Dr. Perlmutter’s research at Berkeley Lab since 1983. After the introduction from Secretary of Energy Steven Chu, Dr. Perlmutter delivered a presentation entitled "Supernovae, DarkEnergy and the Accelerating Universe: How DOE Helped to Win (yet another) Nobel Prize." [Copied with editing from DOE Media Advisory issued January 10th, found at http://energy.gov/articles/energy-department-host-event-2011-physics-nobel-laureate-saul-perlmutter

The Department of Energy (DOE) hosted an event Friday, January 13, with 2011 Physics Nobel Laureate Saul Perlmutter. Dr. Perlmutter, a physicist at the Department’s Lawrence Berkeley National Laboratory and a professor of physics at the University of California at Berkeley, won the 2011 Nobel Prize in Physics “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.” DOE’s Office of Science has supported Dr. Perlmutter’s research at Berkeley Lab since 1983. After the introduction from Secretary of Energy Steven Chu, Dr. Perlmutter delivered a presentation entitled "Supernovae, DarkEnergy and the Accelerating Universe: How DOE Helped to Win (yet another) Nobel Prize." [Copied with editing from DOE Media Advisory issued January 10th, found at http://energy.gov/articles/energy-department-host-event-2011-physics-nobel-laureate-saul-perlmutter

A novel method for extracting cosmological evolution parameters is proposed, using a probe other than light: future observations of the diffuse anti-neutrino flux emitted from core-collapse supernovae (SNe), combined with the SN rate extracted from future SN surveys. The relic SN neutrino differential flux can be extracted by using future neutrino detectors such as Gadolinium-enriched, megaton, water detectors or 100-kiloton detectors of liquid Argon or liquid scintillator. The core-collapse SN rate can be reconstructed from direct observation of SN explosions using future precision observatories. Our method, by itself, cannot compete with the accuracy of the optical-based measurements but may serve as an important consistency check as well as a source of complementary information. The proposal does not require construction of a dedicated experiment, but rather relies on future experiments proposed for other purposes.

The Supernova/Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the darkenergy and alternative explanations of the acceleration of the Universes expansion by performing a series of complementary systematics-controlled astrophysical measurements. We here describe a self-consistent reference mission design that can accomplish this goal with the two leading measurement approaches being the Type Ia supernova Hubble diagram and a wide-area weak gravitational lensing survey. This design has been optimized to first order and is now under study for further modification and optimization. A 2-m three-mirror anastigmat wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high efficiency low-resolution integral field spectrograph. The instrumentation suite provides simultaneous discovery and light-curve measurements of supernovae and then can target individual objects for detailed spectral characterization. The SNAP mission will discover thousands of Type Ia supernovae out to z = 3 and will obtain high-signal-to-noise calibrated light-curves and spectra for a subset of > 2000 supernovae at redshifts between z = 0.1 and 1.7 in a northern field and in a southern field. A wide-field survey covering one thousand square degrees in both northern and southern fields resolves {approx} 100 galaxies per square arcminute, or a total of more than 300 million galaxies. With the PSF stability afforded by a space observatory, SNAP will provide precise and accurate measurements of gravitational lensing. The high-quality data available in space, combined with the large sample of supernovae, will enable stringent control of systematic uncertainties. The resulting data set will be used to determine the energy density of darkenergy and parameters that describe its dynamical behavior. The data also provide a direct test of theoretical models for the darkenergy

The Supernova/Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the darkenergy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled astrophysical measurements. We here describe a self-consistent reference mission design that can accomplish this goal with the two leading measurement approaches being the Type Ia supernova Hubble diagram and a wide-area weak gravitational lensing survey. This design has been optimized to first order and is now under study for further modification and optimization. A 2-m three-mirror anastigmat wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The instrumentation suite provides simultaneous discovery and light-curve measurements of supernovae and then can target individual objects for detailed spectral characterization. The SNAP mission will discover thousands of Type Ia supernovae out to z = 3 and will obtain high-signal-to-noise calibrated light-curves and spectra for a subset of > 2000 supernovae at redshifts between z = 0.1 and 1.7 in a northern field and in a southern field. A wide-field survey covering one thousand square degrees in both northern and southern fields resolves {approx} 100 galaxies per square arcminute, or a total of more than 300 million galaxies. With the PSF stability afforded by a space observatory, SNAP will provide precise and accurate measurements of gravitational lensing. The high-quality data available in space, combined with the large sample of supernovae, will enable stringent control of systematic uncertainties. The resulting data set will be used to determine the energy density of darkenergy and parameters that describe its dynamical behavior. The data also provide a direct test of theoretical models for the dark

The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the darkenergy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, darkenergy density, and ...

In this paper, the holographic darkenergy (HDE) model, where the future event horizon is taken as an IR cut-off, is confronted by using currently available cosmic observational data sets which include type Ia supernovae, baryon acoustic oscillation and cosmic microwave background radiation from full information of WMAP-7yr. Via the Markov Chain Monte Carlo method, we obtain the values of model parameter $c= 0.696_{- 0.0737- 0.132- 0.190}^{+ 0.0736+ 0.159+ 0.264}$ with $1,2,3\\sigma$ regions. Therefore one can conclude that at lest $3\\sigma$ level the future Universe will be dominated by phantom like darkenergy. It is not consistent with positive energy condition, however this condition must be satisfied to derive the holographic bound. It implies that the current cosmic observational data points disfavor the HDE model.

The recent astronomical measurements of distant supernovae as well as other observations indicate that our universe is presently accelerating. There are different proposals for the explanation of this acceleration. Most of these proposals require the existence of exotic matter with negative pressure violating the strong energy condition. On the other hand, there have appeared many models which offer dramatically different mechanism for the current acceleration, in which darkenergy emerges from the gravity sector rather than from the matter sector. In this paper, we compare the concordance $\\Lambda$CDM model with the braneworld models of darkenergy by using Akaike and Bayesian informative critera. We show that, although this model has extra parameters (the fundamental constants of the bulk space) resulting in an improved fit to the SNIa data, these new parameters are actually not important for description of present acceleration epoch. With the example of the Sahni--Shtanov braneworld model \\cite{Shtanov03},...

The property of darkenergy and the physical reason for the acceleration of the present universe are two of the most difficult problems in modern cosmology. The darkenergy contributes about two-thirds of the critical density of the present universe from the observations of type-Ia supernovae (SNe Ia) and anisotropy of cosmic microwave background (CMB). The SN Ia observations also suggest that the universe expanded from a deceleration to an acceleration phase at some redshift, implying the existence of a nearly uniform component of darkenergy with negative pressure. We use the "Gold" sample containing 157 SNe Ia and two recent well-measured additions, SNe Ia 1994ae and 1998aq to explore the properties of darkenergy and the transition redshift. For a flat universe with the cosmological constant,we measure ΩM = 0.28+0.04 -0.05,which is consistent with Riess et al. The transition redshift is zT=0.60+0.06 -0.08. We also discuss several darkenergy models that define w(z) of the parameterized equation of state of darkenergy including one parameter and two parameters (w(z) being the ratio of the pressure to energy density). Our calculations show that the accurately calculated transition redshift varies from zT=0.06+0.07 -0.06 to zT=0.06+0.06 -0.08 across these models. We also calculate the minimum redshift zc at which the current observations need the universe to accelerate.

Scientifically, the WFIRST supernova program is unique: it makes possible a darkenergy measurement that no other space mission or ground-based project is addressing, a measurement that will set the standard in determining the expansion history of the universe continuously from low to high redshifts (0.1 reliable, due to limitations of time the analysis was clearly limited in depth on a number of issues. The objective of this proposal is to further develop this program. Technically this is the WFIRST measurement that arguably requires the most advanced project development, since it requires near-real-time analysis and follow-up with WFIRST, and since it is using the IFU spectrograph in the WFI package, the IFU being the WFIRST instrument that does not yet have a completely consistent set of specifications in the design iteration of the SDT report. In this proposal for the WFIRST Scientific Investigation Team, focused primarily on the supernovadarkenergy measurements, we address these crucial technical needs by bringing the larger supernova community's expertise on the science elements together with a smaller focused team that can produce the specific deliverables. Thus the objectives of this 5 year proposal are the following: 1. Development of scientific performance requirements for the study of DarkEnergy using Type Ia supernovae 2. Design an observing strategy using the Wide Field Instrument (WFI) and the Integral Field Spectrometer Unit (IFU) 3. Development of science data analysis techniques and data analysis software 4. Development of ground and space calibration requirements and estimating realistic correlated errors, both statistical and systematic 5. Development of simulations and data challenges to validate the above 6. Development of complete plans in coordination with WFIRST project, for all aspects of science simulations, precursor observations, ground calibration, observational needs, data processing, anciliary data collection

Darkenergy is one of the mysteries of modern science. It is unlike any known form of matter or energy and has been detected so far only by its gravitational effect of repulsion. Owing to its effects being discernible only at very very large distance scales, darkenergy was only detected at the turn of the last century when technology had advanced enough to observe a greater part of the universe in finer detail. The aim of the report is to gain a better understanding of the mysterious darkenergy. To this end, both theoretical methods and observational evidence are studied. Three lines of evidence, namely , the redshift data of type Ia supernovae, estimates of the age of the universe by various methods, and the anisotropies in the cosmic background radiation, build the case for existence of darkenergy. The supernova data indicate that the expansion of the universe is accelerating. The ages of the oldest star clusters in the universe indicate that the universe is older than previously thought to be. The aniso...

Aims. We investigate the degree of improvement in darkenergy constraints that can be achieved by extending Type Ia Supernova (SN Ia) samples to redshifts z > 1.5 with the Hubble Space Telescope (HST), particularly in the ongoing CANDELS and CLASH multi-cycle treasury programs. Methods. Using the popular CPL parametrization of the darkenergy, w = w0 +wa(1-a), we generate mock SN Ia samples that can be projected out to higher redshifts. The synthetic datasets thus generated are fitted to the CPL model, and we evaluate the improvement that a high-z sample can add in terms of ameliorating the statistical and systematic uncertainties on cosmological parameters. Results. In an optimistic but still very achievable scenario, we find that extending the HST sample beyond CANDELS+CLASH to reach a total of 28 SN Ia at z > 1.0 could improve the uncertainty in the wa parameter by up to 21%. The corresponding improvement in the figure of merit (FoM) would be as high as 28%. Finally, we consider the use of high-redshift SN...

Type Ia supernovae (SNe Ia; exploding white-dwarf stars) were the key to the Nobel-worthy 1998 discovery and subsequent verification that the expansion of the Universe is accelerating, driven by the effects of darkenergy. Understanding the nature of this mysterious, yet dominant, component of the Universe is at the forefront of research in cosmology and fundamental physics. SNe Ia will continue to play a leading role in this enterprise, providing precise cosmological distances that improve constraints on the nature of darkenergy. However, for this effort to succeed, we need to more thoroughly understand relatively nearby SNe Ia, because our conclusions come only from comparisons between them and distant (high-redshift) SNe Ia. Thus, detailed studies of relatively nearby SNe Ia are the focus of this research program. Many interesting results were obtained during the course of this project; these were published in 32 refereed research papers that acknowledged the grant. A major accomplishment was the publication of supernova (SN) rates derived from about a decade of operation of the Lick Observatory Supernova Search (LOSS) with the 0.76-meter Katzman Automatic Imaging Telescope (KAIT). We have determined the most accurate rates for SNe of different types in large, nearby galaxies in the present-day Universe, and these can be compared with SN rates far away (and hence long ago in the past) to set constraints on the types of stars that explode. Another major accomplishment was the publication of the light curves (brightness vs. time) of 165 SNe Ia, along with optical spectroscopy of many of these SNe as well as other SNe Ia, providing an extensive, homogeneous database for detailed studies. We have conducted intensive investigations of a number of individual SNe Ia, including quite unusual examples that allow us to probe the entire range of SN explosions and provide unique insights into these objects and the stars before they explode. My team's studies have also

We present constraints on the darkenergy equation-of-state parameter, w = P/({rho}c{sup 2}), using 60 Type Ia supernovae (SNe Ia) from the ESSENCE supernova survey. We derive a set of constraints on the nature of the darkenergy assuming a flat Universe. By including constraints on ({Omega}{sub M}, w) from baryon acoustic oscillations, we obtain a value for a static equation-of-state parameter w = -1.05{sub -0.12}{sup +0.13} (stat 1{sigma}) {+-} 0.13 (sys) and {Omega}{sub M} = 0.274{sub -0.020}{sup +0.033} (stat 1{sigma}) with a best-fit {chi}{sup 2}/DoF of 0.96. These results are consistent with those reported by the Super-Nova Legacy Survey in a similar program measuring supernova distances and redshifts. We evaluate sources of systematic error that afflict supernova observations and present Monte Carlo simulations that explore these effects. Currently, the largest systematic currently with the potential to affect our measurements is the treatment of extinction due to dust in the supernova host galaxies. Combining our set of ESSENCE SNe Ia with the SuperNova Legacy Survey SNe Ia, we obtain a joint constraint of w = -1.07{sub -0.09}{sup +0.09} (stat 1{sigma}) {+-} 0.13 (sys), {Omega}{sub M} = 0.267{sub -0.018}{sup +0.028} (stat 1{sigma}) with a best-fit {chi}{sup 2}/DoF of 0.91. The current SNe Ia data are fully consistent with a cosmological constant.

We present DES13S2cmm, the first spectroscopically-confirmed superluminous supernova (SLSN) from the DarkEnergy Survey (DES). We briefly discuss the data and search algorithm used to find this event in the first year of DES operations, and outline the spectroscopic data obtained from the European Southern Observatory (ESO) Very Large Telescope to confirm its redshift (z = 0.663 +/- 0.001 based on the host-galaxy emission lines) and likely spectral type (Type I). Using this redshift, we find M-U(peak) = -21.05(-0.09)(+0.10) for the peak, rest-frame U-band absolute magnitude, and find DES13S2cmm to be located in a faint, low-metallicity (subsolar), low stellar-mass host galaxy (log (M/M-circle dot) = 9.3 +/- 0.3), consistent with what is seen for other SLSNe-I. We compare the bolometric light curve of DES13S2cmm to 14 similarly well-observed SLSNe-I in the literature and find that it possesses one of the slowest declining tails (beyond +30 d rest-frame past peak), and is the faintest at peak. Moreover, we find the bolometric light curves of all SLSNe-I studied herein possess a dispersion of only 0.2-0.3 mag between +25 and +30 d after peak (rest frame) depending on redshift range studied; this could be important for 'standardizing' such supernovae, as is done with the more common Type Ia. We fit the bolometric light curve of DES13S2cmm with two competing models for SLSNe-I-the radioactive decay of Ni-56, and a magnetar - and find that while the magnetar is formally a better fit, neither model provides a compelling match to the data. Although we are unable to conclusively differentiate between these two physical models for this particular SLSN-I, further DES observations of more SLSNe-I should break this degeneracy, especially if the light curves of SLSNe-I can be observed beyond 100 d in the rest frame of the supernova.

Full Text Available We apply the new dynamics of 3-space to cosmology by deriving a Hubble expansion solution. This dynamics involves two constants; G and — the fine structure constant. This solution gives an excellent parameter-free fit to the recent supernova and gamma- ray burst redshift data without the need for “dark energy” or “dark matter”. The data and theory together imply an older age for the universe of some 14.7Gyrs. The 3-space dynamics has explained the bore hole anomaly, spiral galaxy flat rotation speeds, the masses of black holes in spherical galaxies, gravitational light bending and lensing, all without invoking “dark matter” or “dark energy”. These developments imply that a new understanding of the universe is now available.

The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely supernovae (SNe) but obtained spectral classifications for just 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 3,073 of these likely SNe and estimate that $\\sim$1,000 are Type Ia SNe (SNe Ia) with light-curve quality sufficient for a cosmological analysis. We use these data with simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the darkenergy equation of state parameter, $w$. Using the method of Bayesian Estimation Applied to Multiple Species (BEAMS), distances to SNe Ia and the contaminating CC SN distribution are simultaneously determined as a function of redshift. We test light-curve based SN classification priors for BEAMS as well as a new classification method that relies upon host galaxy spectra and the association of SN type with host type. By testing several SN classification methods and CC SN parameterizations on 1,000-SN simulations, we conservatively es...

We present DES13S2cmm, the first spectroscopically-confirmed superluminous supernova (SLSN) from the DarkEnergy Survey (DES). We briefly discuss the data and search algorithm used to find this event in the first year of DES operations, and outline the spectroscopic data obtained from the European Southern Observatory (ESO) Very Large Telescope to confirm its redshift (z = 0.663 +/- 0.001 based on the host-galaxy emission lines) and likely spectral type (type I). Using this redshift, we find M_U_peak = -21.05 +0.10 -0.09 for the peak, rest-frame U-band absolute magnitude, and find DES13S2cmm to be located in a faint, low metallicity (sub-solar), low stellar-mass host galaxy (log(M/M_sun) = 9.3 +/- 0.3); consistent with what is seen for other SLSNe-I. We compare the bolometric light curve of DES13S2cmm to fourteen similarly well-observed SLSNe-I in the literature and find it possesses one of the slowest declining tails (beyond +30 days rest frame past peak), and is the faintest at peak. Moreover, we find the b...

We present Advanced Camera for Surveys, NICMOS, and Keck adaptive-optics-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Of these SNe Ia, 14 pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on darkenergy. Of our new SNe Ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zero point at the count rates appropriate for very distant SNe Ia. Adding these SNe improves the best combined constraint on dark-energy density, {rho}{sub DE}(z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat {Lambda}CDM universe, we find {Omega}{sub {Lambda}} = 0.729 {+-} 0.014 (68% confidence level (CL) including systematic errors). For a flat wCDM model, we measure a constant dark-energy equation-of-state parameter w = -1.013{sup +0.068}{sub -0.073} (68% CL). Curvature is constrained to {approx}0.7% in the owCDM model and to {approx}2% in a model in which darkenergy is allowed to vary with parameters w{sub 0} and w{sub a} . Further tightening the constraints on the time evolution of darkenergy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union.

We present a study of quasar selection using the supernova fields of the DarkEnergy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid-IR W1-W2 color, a mixture of WISE and DES colors (g ‑ i and i-W1), and a mixture of Vista Hemisphere Survey and DES colors (g ‑ i and i ‑ K). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ 2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i 85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg2 of the DES supernova fields. The catalog includes quasars with redshifts up to z ∼ 4 and brighter than i = 22 mag, although the catalog is not complete up to this magnitude limit.

The Pan-STARRS (PS1) Medium Deep Survey discovered over 5,000 likely supernovae (SNe) but obtained spectral classifications for just 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 2,979 of these likely SNe and estimate that ˜1,100 are Type Ia SNe (SNe Ia) with light-curve quality sufficient for a cosmological analysis. We then use these data with simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the darkenergy equation of state, w. With the method of Bayesian Estimation Applied to Multiple Species (BEAMS), we can simultaneously determine distances to SNe Ia and the contaminating CC SN distribution as a function of redshift. We use light-curve based SN classification priors for BEAMS as well as a new classification method based on host galaxy spectra and the association of SN type with host type. From simulations of 1,000 PS1 SNe, we find that w is biased by just -0.005 due to CC SN contamination, 10% of its statistical uncertainty. By applying several independent SN classification methods and CC SN parameterizations, we estimate w can be measured with a systematic error of 0.014, 30% of the statistical uncertainty on w. We find that BEAMS determines the SALT2 color and shape coefficients, α and β, and the SNIa dispersion with ~1σ bias. We also draw Monte Carlo samples from real PS1 SNe without spectroscopic classifications and find measurements of w from these SNe are fully consistent with the PS1 spectroscopic sample. Finally, the abundance of bright CC SNe in our sample implies that the luminosity functions of Ia-like CC SNe may be ~1 mag brighter than expected from previous measurements.

An overview is presented of a recently proposed "radically conservative" solution to the problem of darkenergy in cosmology. The proposal yields a model universe which appears to be quantitatively viable, in terms of its fit to supernovae luminosity distances, the angular scale of the sound horizon in the cosmic microwave background (CMB) anisotropy spectrum, and the baryon acoustic oscillation scale. It may simultaneously resolve key anomalies relating to primordial lithium abundances, CMB ellipticity, the expansion age of the universe and the Hubble bubble feature. The model uses only general relativity, and matter obeying the strong energy condition, but revisits operational issues in interpreting average measurements in our presently inhomogeneous universe, from first principles. The present overview examines both the foundational issues concerning the definition of gravitational energy in a dynamically expanding space, the quantitative predictions of the new model and its best-fit cosmological parameter...

We combine the CfA3 supernovae Type Ia (SN Ia) sample with samples from the literature to calculate improved constraints on the darkenergy equation of state parameter, w. The CfA3 sample is added to the Union set of Kowalski et al. to form the Constitution set and, combined with a BAO prior, produces 1 + w = 0.013{sub -0.068}{sup +0.066} (0.11 syst), consistent with the cosmological constant. The CfA3 addition makes the cosmologically useful sample of nearby SN Ia between 2.6 and 2.9 times larger than before, reducing the statistical uncertainty to the point where systematics play the largest role. We use four light-curve fitters to test for systematic differences: SALT, SALT2, MLCS2k2 (R{sub V} = 3.1), and MLCS2k2 (R{sub V} = 1.7). SALT produces high-redshift Hubble residuals with systematic trends versus color and larger scatter than MLCS2k2. MLCS2k2 overestimates the intrinsic luminosity of SN Ia with 0.7 < {Delta} < 1.2. MLCS2k2 with R{sub V} = 3.1 overestimates host-galaxy extinction while R{sub V} {approx} 1.7 does not. Our investigation is consistent with no Hubble bubble. We also find that, after light-curve correction, SN Ia in Scd/Sd/Irr hosts are intrinsically fainter than those in E/S0 hosts by 2{sigma}, suggesting that they may come from different populations. We also find that SN Ia in Scd/Sd/Irr hosts have low scatter (0.1 mag) and reddening. Current systematic errors can be reduced by improving SN Ia photometric accuracy, by including the CfA3 sample to retrain light-curve fitters, by combining optical SN Ia photometry with near-infrared photometry to understand host-galaxy extinction, and by determining if different environments give rise to different intrinsic SN Ia luminosity after correction for light-curve shape and color.

We report the discovery of the eighth and ninth known Trojans in stable orbits around Neptune's leading Lagrange point, L4. The objects 2014 QO$_{441}$ and 2014 QP$_{441}$ were detected in data obtained during the 2013-14 and 2014-15 observing seasons by the DarkEnergy Survey, using the DarkEnergy Camera (DECam) on the 4-meter Blanco telescope at Cerro Tololo Inter-American Observatory. Both are in high-inclination orbits (18.8$^{\\circ}$ and 19.4$^{\\circ}$ respectively). With an eccentricity of 0.104, 2014 QO$_{441}$ has the most eccentric orbit of the eleven known stable Neptune Trojans. Here we describe the search procedure and investigate the objects' long-term dynamical stability and physical properties.

As a solution to the well-known problem that the shock wave potentially responsible for the explosion of a supernova actually tends to stall, we propose a new energy source arising from our model for dark matter. Our earlier model proposed that dark matter should consist of cm-large white dwarf-like objects kept together by a skin separating two different sorts of vacua. These dark matter balls or pearls will collect in the middle of any star throughout its lifetime. At some stage during the development of a supernova the balls will begin to take in neutrons and then other surrounding material. By passing into a ball nucleons fall through a potential of order 10 MeV, causing a severe production of heat - of order 10 foe for a solar mass of material eaten by the balls. The temperature in the iron core will thereby be raised, splitting up the iron into smaller nuclei. This provides a mechanism for reviving the shock wave when it arrives and making the supernova explosion really occur. The onset of the heating d...

We combine measurements of weak gravitational lensing from the CFHTLS-Wide survey, supernovae Ia from CFHT SNLS and CMB anisotropies from WMAP5 to obtain joint constraints on cosmological parameters, in particular, the darkenergy equation of state parameter w. We assess the influence of systematics in the data on the results and look for possible correlations with cosmological parameters. We implement an MCMC algorithm to sample the parameter space of a flat CDM model with a dark-energy component of constant w. Systematics in the data are parametrised and included in the analysis. We determine the influence of photometric calibration of SNIa data on cosmological results by calculating the response of the distance modulus to photometric zero-point variations. The weak lensing data set is tested for anomalous field-to-field variations and a systematic shape measurement bias for high-z galaxies. Ignoring photometric uncertainties for SNLS biases cosmological parameters by at most 20% of the statistical errors, ...

We present observational constraints on the nature of darkenergy using the Supernova Legacy Survey three year sample (SNLS3) of Guy et al. (2010) and Conley et al. (2011). We use the 472 SNe Ia in this sample, accounting for recently discovered correlations between SN Ia luminosity and host galaxy properties, and include the effects of all identified systematic uncertainties directly in the cosmological fits. Combining the SNLS3 data with the full WMAP7 power spectrum, the Sloan Digital Sky Survey luminous red galaxy power spectrum, and a prior on the Hubble constant H0 from SHOES, in a flat universe we find omega_m=0.269+/-0.015 and w=-1.061+0.069-0.068 -- a 6.5% measure of the darkenergy equation-of-state parameter w. The statistical and systematic uncertainties are approximately equal, with the systematic uncertainties dominated by the photometric calibration of the SN Ia fluxes -- without these calibration effects, systematics contribute only a ~2% error in w. When relaxing the assumption of flatness, w...

The transit of primordial black holes through a white dwarf causes localized heating around the trajectory of the black hole through dynamical friction. For sufficiently massive black holes, this heat can initiate runaway thermonuclear fusion causing the white dwarf to explode as a supernova. The shape of the observed distribution of white dwarfs with masses up to $1.25 M_{\\odot}$ rules out primordial black holes with masses $\\sim 10^{19}$ gm - $10^{20}$ gm as a dominant constituent of the local dark matter density. Black holes with masses as large as $10^{24}$ gm will be excluded if recent observations by the NuStar collaboration of a population of white dwarfs near the galactic center are confirmed. Black holes in the mass range $10^{20}$ gm - $10^{22}$ gm are also constrained by the observed supernova rate, though these bounds are subject to astrophysical uncertainties. These bounds can be further strengthened through measurements of white dwarf binaries in gravitational wave observatories. The mechanism p...

Is the accelerating expansion of the Universe true, inferred through observations of distant supernovae, and is the implied existence of an enormous amount of anti-gravitational darkenergy material driving the accelerating expansion of the universe also true? To be physically useful these propositions must be falsifiable; that is, subject to observational tests that could render them false, and both fail when viscous, diffusive, astro-biological and turbulence effects are included in the interpretation of observations. A more plausible explanation of negative stresses producing the big bang is turbulence at Planck temperatures. Inflation results from gluon viscous stresses at the strong force transition. Anti-gravitational (darkenergy) turbulence stresses are powerful but only temporary. No permanent darkenergy is needed. At the plasma-gas transition, viscous stresses cause fragmentation of plasma proto-galaxies into dark matter clumps of primordial gas planets, each of which falsifies dark-energy cold-dar...

We describe the DarkEnergy Survey (DES), a proposed optical-near infrared survey of 5000 sq. deg of the South Galactic Cap to ~24th magnitude in SDSS griz, that would use a new 3 sq. deg CCD camera to be mounted on the Blanco 4-m telescope at Cerro Telolo Inter-American Observatory (CTIO). The survey data will allow us to measure the darkenergy and dark matter densities and the darkenergy equation of state through four independent methods: galaxy clusters, weak gravitational lensing tomography, galaxy angular clustering, and supernova distances. These methods are doubly complementary: they constrain different combinations of cosmological model parameters and are subject to different systematic errors. By deriving the four sets of measurements from the same data set with a common analysis framework, we will obtain important cross checks of the systematic errors and thereby make a substantial and robust advance in the precision of darkenergy measurements.

For 70 years, the physics community operated under the assumption that the expansion of the Universe must be slowing due to gravitational attraction. Then, in 1998, two teams of scientists used Type Ia supernovae to discover that cosmic expansion was actually acceler- ating due to a mysterious "darkenergy." As a result, Type Ia supernovae have become the most cosmologically important transient events in the last 20 years, with a large amount of effort going into their discovery as well as understanding their progenitor systems. One such probe for understanding Type Ia supernovae is to use rate measurements to de- termine the time delay between star formation and supernova explosion. For the last 30 years, the discovery of individual Type Ia supernova events has been accelerating. How- ever, those discoveries were happening in time-domain surveys that probed only a portion of the redshift range where expansion was impacted by darkenergy. The DarkEnergy Survey (DES) is the first project in the "next generation" of time-domain surveys that will discovery thousands of Type Ia supernovae out to a redshift of 1.2 (where darkenergy be- comes subdominant) and DES will have better systematic uncertainties over that redshift range than any survey to date. In order to gauge the discovery effectiveness of this survey, we will use the first season's 469 photometrically typed supernovee and compare it with simulations in order to update the full survey Type Ia projections from 3500 to 2250. We will then use 165 of the 469 supernovae out to a redshift of 0.6 to measure the supernovae rate both as a function of comoving volume and of the star formation rate as it evolves with redshift. We find the most statistically significant prompt fraction of any survey to date (with a 3.9? prompt fraction detection). We will also reinforce the already existing tension in the measurement of the delayed fraction between high (z > 1.2) and low red- shift rate measurements, where we find no

In this paper, we investigate the Ricci darkenergy model with perturbations through the joint constraints of current cosmological data sets from dynamical and geometrical perspectives. We use the full cosmic microwave background information from WMAP seven-year data, the baryon acoustic oscillations from the Sloan Digital Sky Survey and the Two Degree Galaxy Redshift Survey, and type Ia supernovae from the Union2 compilation of the Supernova Cosmology Project Collaboration. A global constraint is performed by employing the Markov chain Monte Carlo method. With the best-fitting results, we show the differences of cosmic microwave background power spectra and background evolutions for the cosmological constant model and Ricci darkenergy model with perturbations.

The Pan-STARRS (PS1) Medium Deep Survey discovered over 5000 likely supernovae (SNe) but obtained spectral classifications for just 10% of its SN candidates. We measured spectroscopic host galaxy redshifts for 3147 of these likely SNe and estimate that ˜1000 are Type Ia SNe (SNe Ia) with light-curve quality sufficient for a cosmological analysis. We use these data with simulations to determine the impact of core-collapse SN (CC SN) contamination on measurements of the darkenergy equation of state parameter, w. Using the method of Bayesian Estimation Applied to Multiple Species (BEAMS), distances to SNe Ia and the contaminating CC SN distribution are simultaneously determined. We test light-curve-based SN classification priors for BEAMS as well as a new classification method that relies upon host galaxy spectra and the association of SN type with host type. By testing several SN classification methods and CC SN parameterizations on large SN simulations, we estimate that CC SN contamination gives a systematic error on w ({σ }w{CC}) of 0.014, 29% of the statistical uncertainty. Our best method gives {σ }w{CC}=0.004, just 8% of the statistical uncertainty, but could be affected by incomplete knowledge of the CC SN distribution. This method determines the SALT2 color and shape coefficients, α and β, with ˜3% bias. However, we find that some variants require α and β to be fixed to known values for BEAMS to yield accurate measurements of w. Finally, the inferred abundance of bright CC SNe in our sample is greater than expected based on measured CC SN rates and luminosity functions.

We present a study of quasar selection using the DES supernova fields. We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. We only considered objects that appear as point sources in the DES images. We examine color selection methods based on the WISE mid-IR W1-W2 color, a mixture of WISE and DES colors (g-i and i-W1) and a mixture of VHS and DES colors (g-i and i-K). For probabilistic quasar selection, we used XDQSOz, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band chi2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection band...

Recent studies of low redshift type Ia supernovae (SNIa) indicate that half explode from less than Chandrasekhar mass white dwarfs, implying ignition must proceed from something besides the canonical criticality of Chandrasekhar mass SNIa progenitors. We show that $0.1-10$ PeV mass asymmetric dark matter, with imminently detectable nucleon scattering interactions, can accumulate to the point of self-gravitation in a white dwarf and collapse, shedding gravitational potential energy by scattering off nuclei, thereby heating the white dwarf and igniting the flame front that precedes SNIa. We combine data on SNIa masses with data on the ages of SNIa-adjacent stars. This combination reveals a $ 3 \\sigma$ inverse correlation between SNIa masses and ignition ages, which could result from increased capture of dark matter in 1.4 versus 1.1 solar mass white dwarfs. Future studies of SNIa in galactic centers will provide additional tests of dark-matter-induced type Ia ignition. Remarkably, both bosonic and fermionic SNI...

We present a study of quasar selection using the DES supernova fields. We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. We only considered objects that appear as point sources in the DES images. We examine color selection methods based on the WISE mid-IR W1-W2 color, a mixture of WISE and DES colors (g-i and i-W1) and a mixture of VHS and DES colors (g-i and i-K). For probabilistic quasar selection, we used XDQSOz, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band chi2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i<19.8 mag and i<22 mag. For sources with W1 and W2 detections, the W1-W2 color or XDQSOz method combined with variability gives the highest completenesses of >85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1,263 spectroscopically-confirmed quasars taken by the OzDES survey. The catalog includes quasars with redshifts up to z~4 and brighter than i=22 mag, although the catalog is not complete up this magnitude limit.

"Observations continue to indicate that the Universe is dominated by invisible components - dark matter and darkenergy. Shedding light on this cosmic darkness is a priority for astronomers and physicists" (3 pages)

The nature of darkenergy is of such fundamental importance -- yet such a mystery -- that a dedicated darkenergy experiment should be as comprehensive and powerfully incisive as possible. The Supernova/Acceleration Probe robustly controls for a wide variety of systematic uncertainties, employing the Type Ia supernova distance method, with high signal to noise light curves and spectra over the full redshift range from z=0.1-1.7, and the weak gravitational lensing method with an accurate and stable point spread function.

The nature of darkenergy is of such fundamental importance -- yet such a mystery -- that a dedicated darkenergy experiment should be as comprehensive and powerfully incisive as possible. The Supernova/Acceleration Probe robustly controls for a wide variety of systematic uncertainties, employing the Type Ia supernova distance method, with high signal to noise light curves and spectra over the full redshift range from z=0.1-1.7, and the weak gravitational lensing method with an accurate and stable point spread function.

We revisit constraints on dark photons with masses below ~ 100 MeV from the observations of Supernova 1987A. If dark photons are produced in sufficient quantity, they reduce the amount of energy emitted in the form of neutrinos, in conflict with observations. For the first time, we include the effects of finite temperature and density on the kinetic-mixing parameter, epsilon, in this environment. This causes the constraints on epsilon to weaken with the dark-photon mass below ~ 15 MeV. For large-enough values of epsilon, it is well known that dark photons can be reabsorbed within the supernova. Since the rates of reabsorption processes decrease as the dark-photon energy increases, we point out that dark photons with energies above the Wien peak can escape without scattering, contributing more to energy loss than is possible assuming a blackbody spectrum. Furthermore, we estimate the systematic uncertainties on the cooling bounds by deriving constraints assuming one analytic and four different simulated temper...

We present ACS, NICMOS, and Keck AO-assisted photometry of 20 Type Ia supernovae SNe Ia from the HST Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on HST.

A physical mechanism that produces three energy components is proposed as the common origin of darkenergy and dark matter. The first two have equations of state W ~ 0 and act like dark matter, while the last has W ~ -1 at low redshifts making it a candidate for darkenergy. These are used to model the supernovae Union2 data resulting in a curve fitting identical to the LAMBDACDM model. This model opens new avenues for Cosmology research and implies a re-interpretation of the dark components as a scalar field stored in the metric of spacetime.

There are many kinds of models which describe the dynamics of darkenergy (DE). Among all we adopt an equation of state (EoS) which varies as a function of time. We adopt Markov Chain Monte Carlo method to constrain the five parameters of our models. As a consequence, we can show the characteristic behavior of DE during the evolution of the universe. We constrain the EoS of DE with use of the avairable data of gamma-ray bursts and type Ia supernovae (SNe Ia) concerning the redshift-luminosity distance relations. As a result, we find that DE is quintessence-like in the early time and phantom-like in the present epoch or near the future, where the change occurs rather rapidly at $z\\sim0.3$.

A new darkenergy model, named "agegraphic darkenergy", has been proposed recently, based on the so-called K\\'{a}rolyh\\'{a}zy uncertainty relation, which arises from quantum mechanics together with general relativity. In this note, we extend the original agegraphic darkenergy model by including the interaction between agegraphic darkenergy and pressureless (dark) matter. In the interacting agegraphic darkenergy model, there are many interesting features different from the original agegrap...

The DarkEnergy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the DarkEnergy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250 micron thick fully-depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2kx4k CCDs for imaging and 12 2kx2k CCDs for guiding and focus. The CCDs have 15 microns x15 microns pixels with a plate scale of 0.263 arc sec per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construct...

The DarkEnergy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the DarkEnergy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

We live in a Universe that is getting bigger faster. This astonishing discovery of Universal acceleration was made in the late 1990s by two teams who made observations of a special type of exploded star known as a `Supernova Type Ia'. (SNeIa) Since the discovery of the accelerating Universe, one of the biggest questions in modern cosmology has been to determine the cause of that acceleration - the answer to this question will have far reaching implications for our theories of cosmology and fundamental physics more broadly. The two main competing explanations for this apparent late time acceleration of the Universe are modified gravity and darkenergy. The DarkEnergy Survey (DES) has been designed and commissioned to find to find answers to these questions about the nature of darkenergy and modified gravity. The new 570 megapixel DarkEnergy Camera is currently operating with the Cerro-Tololo Inter American Observatory's 4m Blanco teleccope, carrying out a systematic search for SNeIa, and mapping out the large scale structure of the Universe by making observations of galaxies. The DES science program program which saw first light in September 2013 will run for five years in total. DES SNeIa data in combination with the other DES observations of large scale structure will enable us to put increasingly accurate constraints on the expansion history of the Universe and will help us distinguish between competing theories of darkenergy and modified gravity. As we draw to the close of the first observing season of DES in March 2014, we will report on the current status of the DES supernova survey, presenting first year supernovae data, preliminary results, survey strategy, discovery pipeline, spectroscopic target selection and data quality. This talk will give the first glimpse of the DES SN first year data and initial results as we begin our five year survey in search of darkenergy. On behalf of the DarkEnergy Survey collaboration.

In this paper, we use the joint measurement of geometry and growth rate from matter density perturbations to constrain the holographic darkenergy model. The geometry measurement includes type Ia supernovae (SN Ia) Union2.1, full information of cosmic microwave background (CMB) from WMAP-7yr and baryon acoustic oscillation (BAO). For the growth rate of matter density perturbations, the results $f(z)\\sigma_8(z)$ measured from the redshift-space distortion (RSD) in the galaxy power spectrum are employed. Via the Markov Chain Monte Carlo method, we try to constrain the model parameters space. The jointed constraint shows that $c=0.750_{- 0.0999- 0.173- 0.226}^{+ 0.0976+ 0.215+ 0.319}$ and $\\sigma_8=0.763_{- 0.0465- 0.0826- 0.108}^{+ 0.0477+ 0.0910+ 0.120}$ with $1,2,3\\sigma$ regions. After marginalizing the other irrelevant model parameters, we show the evolution of the equation of state of HDE with respect to the redshift $z$. Though the current cosmic data points favor a phantom like HDE Universe for the mean ...

We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to trace the history of cosmic expansion over the last 10 billion years. These objects, which include 13 spectroscopically confirmed SNe Ia at z > 1, were discovered during 14 epochs of reimaging of the GOODS fields North and South over two years with the Advanced Camera for Surveys on HST. Together with a recalibration of our previous HST-discovered SNe Ia, the full sample of 23 SNe Ia at z > 1 provides the highest-redshift sample known. Combined with previous SN Ia datasets, we measured H(z) at discrete, uncorrelated epochs, reducing the uncertainty of H(z>1) from 50% to under 20%, strengthening the evidence for a cosmic jerk--the transition from deceleration in the past to acceleration in the present. The unique leverage of the HST high-redshift SNe Ia provides the first meaningful constraint on the darkenergy equation-of-state parameter at z >1. The result remains consistent with a cosmological ...

We investigate a phenomenological non-gravitational coupling between darkenergy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to darkenergy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both mode...

The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating supernovae dimness, suggesting a remarkable change in the expansion rate of the Universe from a decrease since the big bang to an increase, driven by anti-gravity forces of a mysterious darkenergy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and darkenergy concepts. Kinematic viscosity is neglected in current standard models of self-gr...

This overview paper describes the legacy prospect and discovery potential of the DarkEnergy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize darkenergy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from ‘Science Verification’, and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

I discuss the darkenergy characterized by the violation of the null energy condition ($\\varrho + p \\geq 0$), dubbed phantom. Amazingly, it is admitted by the current astronomical data from supernovae. We discuss both classical and quantum cosmological models with phantom as a source of matter and present the phenomenon called phantom duality.

In this talk I will firstly review on the current constraints on the equation of state of the darkenergy from observational data, then present a new scenario of darkenergy dubbed {\\it Quintom}. The recent fits to the type Ia supernova data and the cosmic microwave background and so on in the literature find that the behavior of darkenergy is to great extent in consistency with a cosmological constant, however the dynamical darkenergy scenarios are generally not ruled out, and one class of models with an equation of state transiting from below -1 to above -1 as the redshift increases is mildly favored. The second part of the talk is on interacting darkenergy. I will review briefly on the models of neutrino darkenergy.

This overview article describes the legacy prospect and discovery potential of the DarkEnergy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterise darkenergy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasi...

The idea that we live near the centre of a large, non-linear void has attracted attention recently as an alternative to darkenergy or modified gravity. We show that an appropriate void profile can fit both the latest cosmic microwave background and supernova data. However, this requires either a fine-tuned primordial spectrum or a Hubble rate so low as to rule these models out. We also show that measurements of the radial baryon acoustic scale can provide very strong constraints. Our results present a serious challenge to void models of acceleration.

It is now well accepted that both Dark Matter and DarkEnergy are required in any successful cosmological model. Although there is ample evidence that both Dark components are necessary, the conventional theories make no prediction for the contributions from each of them. Moreover, there is usually no intrinsic relationship between the two components, and no understanding of the nature of the mysteries of the Dark Sector. Here we suggest that if the Dark Side is so seductive then we should not be restricted to just 2 components. We further suggest that the most natural model has 5 distinct forms of DarkEnergy in addition to the usual Dark Matter, each contributing precisely equally to the cosmic energy density budget.

Gravity should halt the expansion of the universe but a few years ago a study of supernovae showed that in fact cosmic expansion is speeding up. To explain this, cosmologists have postulated that a strange, repulsive force, which they call darkenergy, is at work, counteracting gravity and pushing galaxies apart at an accelerating rate (1/2 page).

We build a model of metastable darkenergy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable darkenergy is also embedded into a model with $SU(2)_R$ symmetry. The darkenergy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the darkenergy particle into (cold and warm) dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and darkenergy, and the model opens a new window to investigate the dark secto...

Full Text Available We build a model of metastable darkenergy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable darkenergy is also embedded into a model with SU(2R symmetry. The darkenergy doublet and the dark matter doublet naturally interact with each other. A three-body decay of the darkenergy particle into (cold and warm dark matter can be as long as large fraction of the age of the universe, if the mediator is massive enough, the lower bound being at intermediate energy level some orders below the grand unification scale. Such a decay shows a different form of interaction between dark matter and darkenergy, and the model opens a new window to investigate the dark sector from the point-of-view of particle physics.

Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.

Darkenergy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the darkenergy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar field models) which is often generically called "darkenergy". We then use the approximate solutions to look at the impact of the darkenergy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.

In cosmology we are facing the darkenergy crisis: How can we survive huge vacuum energy, meanwhile living with tiny darkenergy? For the solution to this crisis, we raise several clues and hints, in particular, supersymmetry and the double hierarchy, M{sub p}-M{sub SM}-M{sub DE} (Planck-Standard Model-darkenergy scales). These two clues naturally lead to a solution with a supersymmetry-breaking brane-world. The train of thought from the clues to the solution is elucidated.

In this work Gamma Ray Burst (GRB) data is used to place constraints on a putative coupling between darkenergy and dark matter. Type Ia supernovae (SNe Ia) constraints from the Sloan Digital Sky Survey II (SDSS-II) first-year results, the cosmic microwave background radiation (CMBR) shift parameter from WMAP seven year results and the baryon acoustic oscillation (BAO) peak from the Sloan Digital Sky Survey (SDSS) are also discussed. The prospects for the field are assessed, as more GRB events become available.

We discuss the intriguing possibility that darkenergy may change its equation of state in situations where large darkenergy fluctuations are present. We show indications of this dynamical mutation in some generic models of darkenergy.

Different holographic dark-energy models are studied from a unifying point of view. We compare models for which the Hubble scale, the future event horizon or a quantity proportional to the Ricci scale are taken as the infrared cutoff length. We demonstrate that the mere definition of the holographic dark-energy density generally implies an interaction with the dark-matter component. We discuss the relation between the equation-of-state parameter and the energy density ratio of both components for each of the choices, as well as the possibility of noninteracting and scaling solutions. Parameter estimations for all three cutoff options are performed with the help of a Bayesian statistical analysis, using data from supernovae type Ia and the history of the Hubble parameter. The ΛCDM model is the clear winner of the analysis. According to the Bayesian information criterion (BIC), all holographic models should be considered as ruled out, since the difference ΔBIC to the corresponding ΛCDM value is >10. According to the Akaike information criterion (AIC), however, we find ΔAIC<2 for models with Hubble-scale and Ricci-scale cutoffs, indicating, that they may still be competitive. As we show for the example of the Ricci-scale case, also the use of certain priors, reducing the number of free parameters to that of the ΛCDM model, may result in a competitive holographic model.

Giving rise to a new and exciting research field, observations of the last 13 years established the accelerated expansion of the Universe. This is a strong indication of new physics, either in the form of a new energy component of the Universe -- darkenergy -- or of theories of gravity beyond general relativity. A powerful approach to this problem is the study of complementary cosmological probes in large optical galaxy surveys such as the DarkEnergy Survey (DES). We present the expectations for darkenergy physics based on the combination of four fundamental probes: galaxy clusters, weak lensing, large scale structure and supernovae. We show that DES data have constraining power to improve current measurements of the darkenergy equation-of-state parameter by a factor of 3--5 and to distinguish between general relativity and modified gravity scenarios.

By careful analysis of the data from the WMAP satellite, scientists were surprised to determine that about 70% of the matter in our universe is in some unknown form, and labeled it DarkEnergy. Earlier, in 1998, two separate international groups of astronomers studying Ia supernovae were even more surprised to be forced to conclude that an amazing smooth transition occurred, from the expected slowing down of the expansion of our universe (due to normal positive gravitation) to an accelerating expansion of the universe that began at at a big bang age of the universe of about nine billion years. In 1918 Albert Einstein stated that his Lambda term in his theory of general relativity was ees,``the energy of empty space,'' and represented a negative pressure and thus a negative gravity force. However my 2004 ``Strong'' Magnetic Field model (SMF) for the origin of magnetic fields at Combination Time (Astro-ph0509223 and 0509222) in our big bang universe produces a unique topology for Superclusters, having almost all the mass, visible and invisible, i.e. from clusters of galaxies down to particles with mass, on the surface of an ellipsoid surrounding a growing very high vacuum. If I hypothesize, with Einstein, that there exists a constant ees force per unit volume, then, gradually, as the universe expands from Combination Time, two effects occur (a) the volume of the central high vacuum region increases, and (b) the density of positive gravity particles in the central region of each Supercluster in our universe decreases dramatically. Thus eventually Einstein's general relativity theory's repulsive gravity of the central very high vacuum region becomes larger than the positive gravitational attraction of all the clusters of galaxies, galaxies, quasars, stars and plasma on the Supercluster shell, and the observed accelerating expansion of our universe occurs. This assumes that our universe is made up mostly of such Superclusters. It is conceivable that the high vacuum

We review the paradigm of holographic darkenergy (HDE), which arises from a theoretical attempt of applying the holographic principle (HP) to the darkenergy (DE) problem. Making use of the HP and the dimensional analysis, we derive the general formula of the energy density of HDE. Then, we describe the properties of HDE model, in which the future event horizon is chosen as the characteristic length scale. We also introduce the theoretical explorations and the observational constraints for this model. Next, in the framework of HDE, we discuss various topics, such as spatial curvature, neutrino, instability of perturbation, time-varying gravitational constant, inflation, black hole and big rip singularity. In addition, from both the theoretical and the observational aspects, we introduce the interacting holographic darkenergy scenario, where the interaction between dark matter and HDE is taken into account. Furthermore, we discuss the HDE scenario in various modified gravity (MG) theories, such as Brans-Dick...

We consider cosmological tests of a scalar-vector-tensor gravitational model, in which the darkenergy is included in the total action through a gauge invariant, electromagnetic type contribution. The ground state of darkenergy, corresponding to a constant potential $V$ is a Bose-Einstein type condensate with spontaneously broken U(1) symmetry. In another words darkenergy appears as a massive vector field emerging from a superposition of a massless vector and a scalar field, the latter corresponding to the Goldstone boson. Two particular cosmological models, corresponding to pure electric and pure magnetic type potentials, respectively are confronted with Type IA Supernovae and Hubble parameter data. In the electric case good fit is obtained along a narrow inclined stripe in the $\\Omega _{m}-\\Omega _{V}$ parameter plane, which includes the $\\Lambda $CDM limit. The other points on this admissible region represent superconducting darkenergy as a sum of a cosmological constant and a time-evolving contribution...

The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating supernovae dimness, suggesting a remarkable change in the expansion rate of the Universe from a decrease since the big bang to an increase, driven by anti-gravity forces of a mysterious darkenergy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and darkenergy concepts. Kinematic viscosity is neglected in current standard models of self-gravitational structure formation, which rely on cold dark matter CDM condensations and clusterings that are also falsified by fluid mechanics. Weakly collisional CDM particles do not condense but diffuse away. Photon viscosity predicts superclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies ...

We build a model of metastable darkenergy, in which the observed vacuum energy is the value of the scalar potential at the false vacuum. The scalar potential is given by a sum of even self-interactions up to order six. The deviation from the Minkowski vacuum is due to a term suppressed by the Planck scale. The decay time of the metastable vacuum can easily accommodate a mean life time compatible with the age of the universe. The metastable darkenergy is also embedded into a model with $SU(2...

This paper exploits the gravitational magnification of SNe Ia to measure properties of dark matter haloes. The magnification of individual SNe Ia can be computed using observed properties of foreground galaxies and dark matter halo models. We model the dark matter haloes of the galaxies as truncated singular isothermal spheres with velocity dispersion and truncation radius obeying luminosity dependent scaling laws. A homogeneously selected sample of 175 SNe Ia from the first 3-years of the Supernova Legacy Survey (SNLS) in the redshift range 0.2 < z < 1 is used to constrain models of the dark matter haloes associated with foreground galaxies. The best-fitting velocity dispersion scaling law agrees well with galaxy-galaxy lensing measurements. We further find that the normalisation of the velocity dispersion of passive and star forming galaxies are consistent with empirical Faber-Jackson and Tully-Fisher relations, respectively. If we make no assumption on the normalisation of these relations, we find th...

We use Hubble parameter versus redshift data from Stern et al. (2010) and Gaztanaga et al. (2009) to place constraints on model parameters of constant and time-evolving darkenergy cosmological models. These constraints are consistent with (through not as restrictive as) those derived from supernova Type Ia magnitude-redshift data. However, they are more restrictive than those derived from galaxy cluster angular diameter distance, and comparable with those from gamma-ray burst and lookback time data. A joint analysis of the Hubble parameter data with more restrictive baryon acoustic oscillation peak length scale and supernova Type Ia apparent magnitude data favors a spatially-flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude time-varying darkenergy.

Constellation-X, with more than 100 times the collecting area of any previous spectroscopic mission operating in the 0.25-40 keV bandpass, will enable highthroughput, high spectral resolution studies of sources ranging from the most luminous accreting supermassive black holes in the Universe to the disks around young stars where planets form. This talk will review the updated Constellation-X science case, released in booklet form during summer 2005. The science areas where Constellation-X will have major impact include the exploration of the space-time geometry of black holes spanning nine orders of magnitude in mass and the nature of the darkenergy and dark matter which govern the expansion and ultimate fate of the Universe. Constellation-X will also explore processes referred to as "cosmic feedback" whereby mechanical energy, radiation, and chemical elements from star formation and black holes are returned to interstellar and intergalactic medium, profoundly affecting the development of structure in the Universe, and will also probe all the important life cycles of matter, from stellar and planetary birth to stellar death via supernova to stellar endpoints in the form of accreting binaries and supernova remnants. This talk will touch upon all these areas, with particular emphasis on Constellation-X's role in the study of DarkEnergy.

Full Text Available The possible holographic origin of darkenergy is investigated. The main existing explanations, namely the UV/IR connection argument of Cohen et al., Thomas’ bulk holography argument, and Ng’s spacetime foam argument, are shown to be not wholly satisfactory. A new explanation is then proposed based on the ideas of Thomas and Ng. It is suggested that darkenergy originates from the quantum fluctuations of spacetime limited by the event horizon of the universe. Several potential problems of the explanation are also discussed.

The local measurement of H0 is in tension with the prediction of Λ cold dark matter model based on the Planck data. This tension may imply that darkenergy is strengthened in the late-time Universe. We employ the latest cosmological observations on cosmic microwave background, the baryon acoustic oscillation, large-scale structure, supernovae, H(z) and H0 to constrain several interacting darkenergy models. Our results show no significant indications for the interaction between darkenergy and dark matter. The H0 tension can be moderately alleviated, but not totally released.

Darkenergy is an important science driver of many upcoming large-scale surveys. With small, stable seeing and low thermal infrared background, Dome A, Antarctica, offers a unique opportunity for shedding light on fundamental questions about the universe. We show that a deep, high-resolution imaging survey of 10,000 square degrees in \\emph{ugrizyJH} bands can provide competitive constraints on darkenergy equation of state parameters using type Ia supernovae, baryon acoustic oscillations, and weak lensing techniques. Such a survey may be partially achieved with a coordinated effort of the Kunlun Dark Universe Survey Telescope (KDUST) in \\emph{yJH} bands over 5000--10,000 deg$^2$ and the Large Synoptic Survey Telescope in \\emph{ugrizy} bands over the same area. Moreover, the joint survey can take advantage of the high-resolution imaging at Dome A to further tighten the constraints on darkenergy and to measure dark matter properties with strong lensing as well as galaxy--galaxy weak lensing.

We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunches or big rips singularities. Classically these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe. (fast track communication)

From the observed late-time acceleration of cosmic expansion arises the quest for the nature of DarkEnergy. As has been widely discussed, the cosmic neutrino background naturally qualifies for a connection with the DarkEnergy sector and as a result could play a key role for the origin of cosmic acceleration. In this thesis we explore various theoretical aspects and phenomenological consequences arising from non-standard neutrino interactions, which dynamically link the cosmic neutrino background and a slowly-evolving scalar field of the dark sector. In the considered scenario, known as Neutrino DarkEnergy, the complex interplay between the neutrinos and the scalar field not only allows to explain cosmic acceleration, but intriguingly, as a distinct signature, also gives rise to dynamical, time-dependent neutrino masses. In a first analysis, we thoroughly investigate an astrophysical high energy neutrino process which is sensitive to neutrino masses. We work out, both semi-analytically and numerically, the generic clear-cut signatures arising from a possible time variation of neutrino masses which we compare to the corresponding results for constant neutrino masses. Finally, we demonstrate that even for the lowest possible neutrino mass scale, it is feasible for the radio telescope LOFAR to reveal a variation of neutrino masses and therefore to probe the nature of DarkEnergy within the next decade. A second independent analysis deals with the recently challenged stability of Neutrino DarkEnergy against the strong growth of hydrodynamic perturbations, driven by the new scalar force felt between neutrinos. Within the framework of linear cosmological perturbation theory, we derive the equation of motion of the neutrino perturbations in a model-independent way. This equation allows to deduce an analytical stability condition which translates into a comfortable upper bound on the scalar-neutrino coupling which is determined by the ratio of the densities in cold dark

We have investigated interacting darkenergy cosmologies both concerning their impact on the background evolution of the Universe and their effects on cosmological structure growth. For the former aspect, we have developed a cosmological model featuring a matter species consisting of particles with a mass that increases with time. In such model the appearance of a Growing Matter component, which is negligible in early cosmology, dramatically slows down the evolution of the darkenergy scalar field at a redshift around six, and triggers the onset of the accelerated expansion of the Universe, therefore addressing the Coincidence Problem. We propose to identify this Growing Matter component with cosmic neutrinos, in which case the present darkenergy density can be related to the measured average mass of neutrinos. For the latter aspect, we have implemented the new physical features of interacting darkenergy models into the cosmological N-body code GADGET-2, and we present the results of a series of high-resolution simulations for a simple realization of darkenergy interaction. As a consequence of the new physics, cold dark matter and baryon distributions evolve differently both in the linear and in the non-linear regime of structure formation. Already on large scales, a linear bias develops between these two components, which is further enhanced by the non-linear evolution. We also find, in contrast with previous work, that the density profiles of cold dark matter halos are less concentrated in coupled darkenergy cosmologies compared with {lambda}{sub CDM}. Also, the baryon fraction in halos in the coupled models is significantly reduced below the universal baryon fraction. These features alleviate tensions between observations and the {lambda}{sub CDM} model on small scales. Our methodology is ideally suited to explore the predictions of coupled darkenergy models in the fully non-linear regime, which can provide powerful constraints for the viable parameter

This white paper describes the LSST DarkEnergy Science Collaboration (DESC), whose goal is the study of darkenergy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of darkenergy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for darkenergy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of darkenergy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST darkenergy data analysis. The technical working groups make the connection between darkenergy science and the LSST system. The working groups ha...

We investigate a spatially flat Friedmann-Robertson-Walker (FRW) cosmological model with cold dark matter coupled to a darkenergy which is given by the modified holographic Ricci cutoff. The interaction used is linear in both darkenergy densities, the total energy density and its derivative. Using the statistical method of $\\chi^2$-function for the Hubble data, we obtain $H_0=73.6km/sMpc$, $\\omega_s=\\gamma_s -1=-0.842$ for the asymptotic equation of state and $ z_{acc}= 0.89 $. The estimated values of $\\Omega_{c0}$ which fulfill the current observational bounds corresponds to a darkenergy density varying in the range $0.25R < \\ro_x < 0.27R$.

Dark matter detectors that utilize liquid xenon have now achieved tonne-scale targets, giving them sensitivity to all flavours of supernova neutrinos via coherent elastic neutrino-nucleus scattering. Considering for the first time a realistic detector model, we simulate the expected supernova neutrino signal for different progenitor masses and nuclear equations of state in existing and upcoming dual-phase liquid xenon experiments. We show that the proportional scintillation signal (S2) of a dual-phase detector allows for a clear observation of the neutrino signal and guarantees a particularly low energy threshold, while the backgrounds are rendered negligible during the supernova burst. XENON1T (XENONnT and LZ; DARWIN) experiments will be sensitive to a supernova burst up to 25 (35; 65) kpc from Earth at a significance of more than 5 sigma, observing approximately 35 (123; 704) events from a 27 solar-mass supernova progenitor at 10 kpc. Moreover, it will be possible to measure the average neutrino energy of a...

Recently, motivated by the similar one in the framework of General Relativity (GR), Geng et al.} proposed to allow a non-minimal coupling between quintessence and gravity in the framework of teleparallel gravity. They found that this non-minimally coupled quintessence in the framework of teleparallel gravity has a richer structure, and named it "teleparallel darkenergy". In the present work, we note that there might be a deep and unknown connection between teleparallel darkenergy and Elko spinor darkenergy. Motivated by this observation and the previous results of Elko spinor darkenergy, we try to study the dynamics of teleparallel darkenergy. We find that there exist only some dark-energy-dominated de Sitter attractors. No scaling attractor has been found unfortunately. So, similar to Elko spinor darkenergy, teleparallel darkenergy is also plagued with the cosmological coincidence problem, although it has an extra free model parameter $\\xi$.

We consider the cosmological application of Lee-Wick theory where a field has a higher derivative kinetic operators. The higher derivative term can be eliminated by introducing a set of auxiliary fields. We investigate the cosmological evolutions of these fields as a candidate of darkenergy. This model has the same structure as so called ``quintom' model except the form of potentials and the sign of the slope of the potentials. This model can give the stable late time phantom dominated scaling solution ($\\omega_{\\DE} < -1$) or tracking attractors ($\\omega_{\\DE} = 0$) depending on the choice of the slopes of the potential. In order to be a viable darkenergy candidate, the present energy density contrast of darkenergy ($\\Omega_{\\DE}^{(0)}$) should be close to an observed value (0.73) at the same time. However, a simple toy model of the theory can not satisfy both $\\omega_{\\DE}^{(0)} \\simeq -1$ and $\\Omega_{\\DE}^{(0)} = 0.73$. This is also true for any quintom model in literatures unless we suffer from the...

By studying a modified Friedmann equation which arises in an extension of general relativity which accommodates a time-dependent fundamental length $L(t)$, we consider cosmological models where the scale factor diverges with an essential singularity at a finite future time. Such models have no darkenergy in the conventional sense of energy possessing a truly simple pressure-energy relationship. Data on supernovae restrict the time from the present until the Rip to be generically longer than the current age of the Universe.

In this paper, we test the dark matter-darkenergy interacting cosmological model with a dynamic equation of state $w_{DE}(z)=w_{0}+w_{1}z/(1+z)$, using type Ia supernovae (SNe Ia), Hubble parameter data, baryonic acoustic oscillation (BAO) measurements, and the cosmic microwave background (CMB) observation. This interacting cosmological model has not been studied before. The best-fitted parameters with $1 \\sigma$ uncertainties are $\\delta=-0.022 \\pm 0.006$, $\\Omega_{DM}^{0}=0.213 \\pm 0.008$, $w_0 =-1.210 \\pm 0.033$ and $w_1=0.872 \\pm 0.072$ with $\\chi^2_{min}/dof = 0.990$. At the $1 \\sigma$ confidence level, we find $\\delta<0$, which means that the energy transfer prefers from dark matter to darkenergy. We also find that the SNe Ia are in tension with the combination of CMB, BAO and Hubble parameter data. The evolution of $\\rho_{DM}/\\rho_{DE}$ indicates that this interacting model is a good approach to solve the coincidence problem, because the $\\rho_{DE}$ decrease with scale factor $a$. The transition r...

The dark sector of the Universe need not be completely separable into distinct dark matter and darkenergy components. We consider a model of early darkenergy in which the darkenergy mimics a dark matter component in both evolution and perturbations at early times. Barotropic aether darkenergy scales as a fixed fraction, possibly greater than one, of the dark matter density and has vanishing sound speed at early times before undergoing a transition. This gives signatures not only in cosmic...

{\\it The universe is expanding} is known (through Galaxy observations) since 1929 through Hubble's discovery ($V = H D$). Recently in 1999, it is found (through Supernovae observations) that the universe is not simply expanding but is accelerating too. We, however, hardly know only $4\\%$ of the universe. The Wilkinson Microwave Anisotropy Probe (WMAP) satellite observational data suggest $73\\%$ content of the universe in the form of dark-energy, $23\\%$ in the form of non-baryonic dark-matter and the rest $4\\%$ in the form of the usual baryonic matter. The acceleration of the universe is ascribed to this dark-energy with bizarre properties (repulsive-gravity). The question is that whether Hubble's expansion is just due to the shock of big-bang & inflation or it is due to the repulsive-gravity of dark-energy? Now, it is believed to be due to dark-energy, say, by re-introducing the once-discarded cosmological-constant $\\Lambda$. In the present paper, it is shown that `the formula for acceleration due to dark...

Observations of the interstellar medium by the Herschel, Planck etc. infrared satellites throw doubt on standard {\\Lambda}CDMHC cosmological processes to form gravitational structures. According to the Hydro-Gravitational-Dynamics (HGD) cosmology of Gibson (1996), and the quasar microlensing observations of Schild (1996), the dark matter of galaxies consists of Proto-Globular-star-Cluster (PGC) clumps of Earth-mass primordial gas planets in metastable equilibrium since PGCs began star production at 0.3 Myr by planet mergers. Darkenergy and the accelerating expansion of the universe inferred from SuperNovae Ia are systematic dimming errors produced as frozen gas dark matter planets evaporate to form stars. Collisionless cold dark matter that clumps and hierarchically clusters does not exist. Clumps of PGCs began diffusion from the Milky Way Proto-Galaxy upon freezing at 14 Myr to give the Magellanic Clouds and the faint dwarf galaxies of the 10^22 m diameter baryonic dark matter Galaxy halo. The first stars p...

We add Dark Matter DarkEnergy terms with a quintessence field interacting with a Dark Matter field to a MSSM EW Lagrangian previously used to calculate the magnetic field created during the EWPT. From the expectation value of the quintessence field we estimate the Dark Matter mass for parameters used in previous work on Dark Matter-DarkEnergy interactions.

A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "darkenergy," energy associated with empty space. Both dark matter and darkenergy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales.

Distance-redshift data can impose strong constraints on darkenergy models even when the equation of state is oscillatory. Despite the double integral dependence of the distance on the equation of state, precision measurement of the distance-redshift relation for z=0-2 is more incisive than the linear growth factor, CMB last scattering surface distance, and the age of the universe in distinguishing oscillatory behavior from an average behavior. While oscillating models might help solve the coincidence problem (since acceleration occurs periodically), next generation observations will strongly constrain such possibilities.

In this work we have used the recent cosmic chronometer data along with the latest estimation of the local Hubble parameter value, H0 at 2.4% precision as well as the standard darkenergy probes, such as the Supernovae Type Ia, baryon acoustic oscillation distance measurements, and cosmic microwave background measurements (PlanckTT+ lowP ) to constrain a darkenergy model where the darkenergy is allowed to interact with the dark matter. A general equation of state of darkenergy parametrized by a dimensionless parameter "β " is utilized. From our analysis, we find that the interaction is compatible with zero within the 1 σ confidence limit. We also show that the same evolution history can be reproduced by a small pressure of the dark matter.

The coupled darkenergy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as $\\bar{Q}=3H\\xi_x\\bar{\\rho}_x$, which is related to the interaction rate and energy density of darkenergy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, $f\\sigma_8(z)$ data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us the interaction rate is close to zero in 1$\\sigma$ region, it is very hard to distinguish different coupled models from other ones.

We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of darkenergy (DE) with constant equation of state parameter interacting with dark matter (DM). The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. This interaction term describes an exchange of energy flow between the DE and DM within dark sector. To show how the method works we do the reconstruction of the interaction function expanding it in terms of only the first three Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion as well as for the DE equation of the state constant parameter w using the type Ia Supernova SCP Union data set (307 SNe-Ia). The preliminary reconstruction shows that in the best scenario there is an energy transfer from DM to DE which worse...

We present a set of high resolution simulations studying the effect of supernova explosions on magnetized, primordial halos. We focus on the evolution of an initially small-scale magnetic field formed during the collapse of the halo. We vary the degree of magnetization, the halo mass, and the amount of explosion energy in order to account for expected variations as well as to infer systematical dependencies of the results on initial conditions. Our simulations suggest that core collapse supernovae with an explosion energy of 10^51 erg and more violent pair instability supernovae with 10^53 erg are able to disrupt halos with masses up to a few 10^6 and 10^7 M_sun, respectively. The peak of the magnetic field spectra shows a continuous shift towards smaller k-values, i.e. larger length scales, over time reaching values as low as k = 4. On small scales the magnetic energy decreases at the cost of the energy on large scales resulting in well-ordered magnetic field with strengths up to about 10^-8 G depending on t...

We investigate a universe filled with interacting dark matter, holographic darkenergy, and dark radiation for the spatially flat Friedmann-Robertson-Walker (FRW) spacetime. We use a linear interaction to reconstruct all the component energy densities in terms of the scale factor by directly solving the balance's equations along with the source equation. We apply the $\\chi^{2}$ method to the observational Hubble data for constraining the cosmic parameters, contrast with the Union 2 sample of supernovae, and analyze the amount of darkenergy in the radiation era. It turns out that our model exhibits an excess of darkenergy in the recombination era whereas the stringent bound $\\Omega_{\\rm x}(z\\simeq 10^{10})<0.21$ at big-bang nucleosynthesis is fulfilled. We find that the interaction provides a physical mechanism for alleviating the triple cosmic coincidence and this leads to $\\Omega_{\\rm m0}/\\Omega_{\\rm x0} \\simeq \\Omega_{\\rm r0}/\\Omega_{\\rm x0} \\simeq {\\cal O}(1)$.

The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of darkenergy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of darkenergy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of darkenergy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even

We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations to constrain the recently proposed teleparallel darkenergy scenario based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. Using the power-law, the exponential and the inverse hyperbolic cosine potential ansatzes, we show that the scenario is compatible with observations. In particular, the data favor a nonminimal coupling, and although the scalar field is canonical the model can describe both the quintessence and phantom regimes.

We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations to constrain the recently proposed teleparallel darkenergy scenario based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. Using the power-law, the exponential and the inverse hyperbolic cosine potential ansatzes, we show that the scenario is compatible with observations. In particular, the data favor a nonminimal coupling, and although the scalar field is canonical the model can describe both the quintessence and phantom regimes.

The coupling between the dark sectors provides a new approach to mitigate the coincidence problem of cosmological standard model. In this paper, darkenergy is treated as a fluid with a constant equation of state, whose coupling with dark matter is proportional the Hubble parameter and darkenergy density, that is, $Q=3H\\xi_x\\rho_x$. Via combining the background energy transfer and vanishing momentum transfer potential in the frame of either dark matter or darkenergy, we derive the evolution equations for the density and velocity perturbations. Using jointing data sets which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and redshift-space distortion, we perform a full Monte Carlo Markov Chain likelihood analysis for the coupled model. The results show that information provided by $f\\sigma_8(z)$ test significantly enhances the precision of the constraints on the cosmological parameters compared to the case where only geometric measurements are adopted. In part...

[JDEM-Omega is one of the three concepts that contributed to the Wide-Field Infrared Survey Telescope (WFIRST) mission advocated by the Astro2010 Decadal Survey. It is the concept on which the recommended observatory configuration is based.] The Joint DarkEnergy Mission (JDEM) is a space-based observatory designed to perform precision measurements of the nature of darkenergy in the Universe. It will make an order of magnitude progress in measuring the equation of state parameters of the Universe of most importance for understanding darkenergy. JDEM-Omega is a wide-field space telescope operating in the near infrared. Darkenergy measurements will be made via large surveys of galaxies and supernova monitoring. These will be an order of magnitude larger surveys than currently available and will provide enormous catalogs of astrophysical objects for many communities ranging from solar system to galaxy to galaxies/clusters to cosmology. JDEM-Omega is a mission concept collaboratively developed by NASA and the ...

The 2011 Nobel Prize in Physics was awarded for the discovery of accelerating super- novae dimness, suggesting a remarkable reversal in the expansion rate of the Universe from a decrease to an increase, driven by anti-gravity forces of a mysterious darkenergy material comprising 70% of the Universe mass-energy. Fluid mechanics and Herschel- Planck-Spitzer-Hubble etc. space telescope observations falsify both the accelerating ex- pansion rate and darkenergy concepts. Kinematic viscosity is neglected in models of self-gravitational structure formation. Large plasma photon viscosity predicts protosu- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the gas protogalaxies fragment into Earth-mass rogue plan- ets in highly persistent, trillion-planet clumps (proto-globular-star-cluster PGCs). PGC planets freeze to form the dark matter of galaxies and merge to form their stars, giving the hydrogen triple-point (14 K) infrared emissions observed. Darkenergy is a system- atic dimming error for Supernovae Ia caused by partially evaporated planets feeding hot white dwarf stars at the Chandrasekhar carbon limit. Planet atmospheres may or may not dim light from SNe-Ia events depending on the line of sight.

A recently proposed model explains the rise in energy of the positron fraction measured by the PAMELA satellite in terms of hadronic production of positrons in aged supernova remnants, and acceleration therein. Here we present a preliminary calculation of the antiproton flux produced by the same mechanism. While the model is consistent with present data, a rise of the antiproton to proton ratio is predicted at high energy, which strikingly distinguishes this scenario from other astrophysical explanations of the positron fraction (such as pulsars). We briefly discuss important implications for dark matter searches via antimatter.

A recently proposed model (arXiv:0903.2794) explains the rise in energy of the positron fraction measured by the PAMELA satellite in terms of hadronic production of positrons in aged supernova remnants, and acceleration therein. Here we present a preliminary calculation of the anti-proton flux produced by the same mechanism. While the model is consistent with present data, a rise of the antiproton to proton ratio is predicted at high energy, which strikingly distinguishes this scenario from other astrophysical explanations of the positron fraction (like pulsars). We briefly discuss important implications for Dark Matter searches via antimatter.

The physical process leading to the acceleration of the expansion of the universe is unknown. It may involve new high energy physics or extensions to gravitation. Calling this generically darkenergy, we examine the consistencies and relations between these two approaches, showing that an effective equation of state function w(z) is broadly useful in describing the properties of the darkenergy. A variety of cosmological observations can provide important information on the dynamics of darkenergy and the future looks bright for constraining darkenergy, though both the measurements and the interpretation will be challenging. We also discuss a more direct relation between the spacetime geometry and acceleration, via ''geometric darkenergy'' from the Ricci scalar, and superacceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.

The dark sector is described by an additional barotropic fluid which evolves adiabatically during the Universe's history and whose adiabatic exponent γ is derived from the standard definitions of specific heats. Although in general γ is a function of the redshift, the Hubble parameter and its derivatives, we find that our assumptions lead necessarily to solutions with γ =constant in a Friedmann-Lemaître-Robertson-Walker universe. The adiabatic fluid acts effectively as the sum of two distinct components, one evolving like nonrelativistic matter and the other depending on the value of the adiabatic index. This makes the model particularly interesting as a way of simultaneously explaining the nature of both darkenergy and dark matter, at least at the level of the background cosmology. The Λ CDM model is included in this family of theories when γ =0 . We fit our model to supernovae Ia, H (z ) and baryonic acoustic oscillation data, discussing the model selection criteria. The implications for the early Universe and the growth of small perturbations in this model are also discussed.

WASHINGTON -- For the first time, astronomers have clearly seen the effects of "darkenergy" on the most massive collapsed objects in the universe using NASA's Chandra X-ray Observatory. By tracking how darkenergy has stifled the growth of galaxy clusters and combining this with previous studies, scientists have obtained the best clues yet about what darkenergy is and what the destiny of the universe could be. This work, which took years to complete, is separate from other methods of darkenergy research such as supernovas. These new X-ray results provide a crucial independent test of darkenergy, long sought by scientists, which depends on how gravity competes with accelerated expansion in the growth of cosmic structures. Techniques based on distance measurements, such as supernova work, do not have this special sensitivity. Scientists think darkenergy is a form of repulsive gravity that now dominates the universe, although they have no clear picture of what it actually is. Understanding the nature of darkenergy is one of the biggest problems in science. Possibilities include the cosmological constant, which is equivalent to the energy of empty space. Other possibilities include a modification in general relativity on the largest scales, or a more general physical field. People Who Read This Also Read... Chandra Data Reveal Rapidly Whirling Black Holes Ghostly Glow Reveals a Hidden Class of Long-Wavelength Radio Emitters Powerful Nearby Supernova Caught By Web Cassiopeia A Comes Alive Across Time and Space To help decide between these options, a new way of looking at darkenergy is required. It is accomplished by observing how cosmic acceleration affects the growth of galaxy clusters over time. "This result could be described as 'arrested development of the universe'," said Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research. "Whatever is forcing the expansion of the universe to speed up is also forcing its

of the associated gauge group SU(2h is of the order of Λh≃0.3 TeV. One scalar state has zero haplon number and is the resonance observed at the LHC. In addition, there exist new bound states of haplons with no counterpart in the SM, having a mass of the order of 0.5 TeV up to a few TeV. In particular, a neutral scalar state with haplon number 4 is stable and can provide the dark matter in the universe. The QHD, QCD, and QED couplings can unify at the Planck scale. If this scale changes slowly with cosmic time, all of the fundamental couplings, the masses of the nucleons and of the DM particles, including the cosmological term (or vacuum energy density, will evolve with time. This could explain the darkenergy of the universe.

We examine the embedding of darkenergy in high energy models based upon supergravity and extend the usual phenomenological setting comprising an observable sector and a hidden supersymmetry breaking sector by including a third sector leading to the acceleration of the expansion of the universe. We find that gravitational constraints on the non-existence of a fifth force naturally imply that the darkenergy sector must possess an approximate shift symmetry. When exact, the shift symmetry provides an example of a darkenergy sector with a runaway potential and a nearly massless darkenergy field whose coupling to matter is very weak, contrary to the usual lore that darkenergy fields must couple strongly to matter and lead to gravitational inconsistencies. Moreover, the shape of the potential is stable under one-loop radiative corrections. When the shift symmetry is slightly broken by higher order terms in the Kahler potential, the coupling to matter remains small. However, the cosmological dynamics are largel...

The abnormally weighting energy hypothesis consists of assuming that the dark sector of cosmology violates the weak equivalence principle (WEP) on cosmological scales, which implies a violation of the strong equivalence principle for ordinary matter. In this paper, darkenergy is shown to result from the violation of WEP by pressureless (dark) matter. This allows us to build a new cosmological framework in which general relativity is satisfied at low scales, as WEP violation depends on the ratio of the ordinary matter over dark matter densities, but at large scales, we obtain a general relativity-like theory with a different value of the gravitational coupling. This explanation is formulated in terms of a tensor-scalar theory of gravitation without WEP for which there exists a revisited convergence mechanism toward general relativity. The consequent darkenergy mechanism build upon the anomalous gravity of dark matter (i) does not require any violation of the strong energy condition pfairly for supernovae data from various simple couplings and with density parameters very close to the ones of the concordance model ΛCDM, and therefore suggests an explanation to its remarkable adequacy. Finally, (iv) this mechanism ends up in the future with an Einstein de Sitter expansion regime once the attractor is reached.

The acceleration of the expansion of the universe, ascribed to a darkenergy, is one of the most intriguing discoveries in science. In addition to precise, systematics controlled data, clear, robust interpretation of the observations is required to reveal the nature of darkenergy. Even for the simplest question: is the data consistent with the cosmological constant? there are important subtleties in the reconstruction of the darkenergy properties. We discuss the roles of analysis both in terms of the Hubble expansion rate or darkenergy density {rho}DE(z) and in terms of the darkenergy equation of state w(z), arguing that each has its carefully defined place. Fitting the density is best for learning about the density, but using it to probe the equation of state can lead to instability and bias.

The present work is based on the holographic darkenergy model with Hubble horizon as the infrared cut-off. The interaction rate between darkenergy and dark matter has been reconstructed for two different parameterizations of the deceleration parameter. Observational constraints on the model parameters have been obtained by maximum likelihood analysis using the observational Hubble parameter data (OHD), type Ia supernova data (SNe), baryon acoustic oscillation data (BAO) and the distance prior of cosmic microwave background (CMB) namely the CMB shift parameter data (CMBShift). The nature of the darkenergy equation of state parameter has also been studied for the present models. The darkenergy equation of state shows a phantom nature at present. Different information criteria and the Bayesian evidence, which have been invoked in the context of model selection, show that the these two models are at close proximity of each other.

The standard model of cosmology suggests the existence of two components, "dark matter" and "darkenergy", which determine the fate of the Universe. Their nature is still under investigation, and no direct proof of their existences has emerged yet. There exist alternative models which reinterpret the cosmological observations, for example by replacing the darkenergy/dark matter hypothesis by the existence of a unique dark component, the dark fluid, which is able to mimic the behaviour of bot...

We show that current cosmic acceleration can be explained by an almost massless scalar field experiencing quantum fluctuations during primordial inflation. Provided its mass does not exceed the Hubble parameter today, this field has been frozen during the cosmological ages to start dominating the Universe only recently. By using supernovae data, completed with baryonic acoustic oscillations from galaxy surveys and cosmic microwave background anisotropies, we infer the energy scale of primordial inflation to be around a few TeV, which implies a negligible tensor-to-scalar ratio of the primordial fluctuations. Moreover, our model suggests that inflation lasted for an extremely long period. Darkenergy could therefore be a natural consequence of cosmic inflation close to the electroweak energy scale.

We account for the late time acceleration of the Universe by extending the QCD color to a $SU(3)$ invisible sector (IQCD). If the Invisible Chiral symmetry is broken in the early universe, a condensate of dark pions (dpions) and dark gluons (dgluons) forms. The condensate naturally forms due to strong dynamics similar to the Nambu--Jona-Lasinio mechanism. As the Universe evolves from early times to present times the interaction energy between the dgluon and dpion condensate dominates with a negative pressure equation of state and causes late time acceleration. We conclude with a stability analysis of the coupled perturbations of the dark pions and dark gluons.

Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% +/- 1% baryons; 29% +/- 4% cold dark matter; and 66% +/- 6% darkenergy. Now that we have characterized the dark side of the Universe, the challenge is to understand it. The critical questions are: (1) What form do the dark baryons take? (2) What is (are) the constituent(s) of the cold dark matter? (3) What is the nature of the mysterious darkenergy that is causing the Universe to speed up.

We show that the darkenergy effects can be modeled by using an \\emph{Ising perfect fluid} with network interactions, whose low redshift equation of state, i.e. $\\omega_0$, becomes $\\omega_0=-1$ as in the $\\Lambda$CDM model. In our picture, darkenergy is characterized by a barotropic fluid on a lattice in the equilibrium configuration. Thus, mimicking the spin interaction by replacing the spin variable with an occupational number, the pressure naturally becomes negative. We find that the corresponding equation of state mimics the effects of a variable darkenergy term, whose limiting case reduces to the cosmological constant $\\Lambda$. This permits us to avoid the introduction of a vacuum energy as darkenergy source by hand, alleviating the coincidence and fine tuning problems. We find fairly good cosmological constraints, by performing three tests with supernovae Ia, baryonic acoustic oscillation and cosmic microwave background measurements. Finally, we perform the AIC and BIC selection criteria, showing t...

We consider a cosmology in which dark matter and a quintessence scalar field responsible for the acceleration of the Universe are allowed to interact. Allowing for both conformal and disformal couplings, we perform a global analysis of the constraints on our model using Hubble parameter measurements, baryon acoustic oscillation distance measurements, and a Supernovae Type Ia data set. We find that the additional disformal coupling relaxes the conformal coupling constraints. Moreover we show that, at the background level, a disformal interaction within the dark sector is preferred to both $\\Lambda$CDM and uncoupled quintessence, hence favouring interacting darkenergy.

We propose a novel coupled darkenergy model which is assumed to occur as a q-deformed scalar field and investigate whether it will provide an expanding universe phase. We consider the q-deformed darkenergy as coupled to dark matter inhomogeneities. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions. The attractor solutions imply that the coupled q-deformed darkenergy model is consistent with the conventional darkenergy models satisfying an acceleration phase of universe. At the end, we compare the cosmological parameters of deformed and standard darkenergy models and interpret the implications.

We discuss how to formulate a quantum field theory of darkenergy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of darkenergy are strongly constrained. Quintessence-generated long range forces and radiative stability of the quintessence potential require that such dark matter and darkenergy are completely decoupled. However, if darkenergy and a fraction of dar...

Darkenergy and dark matter are only indirectly measured via their gravitational effects. It is possible that there is an exchange of energy within the dark sector, and this offers an interesting alternative approach to the coincidence problem. We consider two broad classes of interacting models where the energy exchange is a linear combination of the dark sector densities. The first class has been previously investigated, but we define new variables and find a new exact solution, which allows for a more direct, transparent and comprehensive analysis. The second class has not been investigated in general form before. We give general conditions on the parameters in both classes to avoid unphysical behavior (such as negative energy densities).

Gravitoectromagnetic Inflation (GI) was introduced to describe in an unified manner, electromagnetic, gravitatory and inflaton fields from a 5D vacuum state. On the other hand, the primordial origin and evolution of darkenergy is today unknown. In this letter we show using GI that the zero modes of some redefined vector fields $B_i=A_i/a$ produced during inflation, could be the source of darkenergy in the universe.

Using recent precision measurements of cosmological paramters, we re-examine whether these observations alone, independent of type Ia supernova surveys, are sufficient to imply the existence of darkenergy. We find that best measurements of the age of the universe $t_0$, the Hubble parameter $H_0$ and the matter fraction $\\Omega_m$ strongly favor an equation of state defined by ($w < -1/3$). This result is consistent with the existence of a repulsive, acceleration-causing component of energy ...

Darkenergy in the universe is assumed to be vacuum energy. The energy-momentum of vacuum is described by a scale-dependent cosmological constant. The equations of motion imply for the density of matter (dust) the sum of the usual matter density (luminous matter) and an additional matter density (dark matter) similar to the darkenergy. The scale-dependent cosmological constant is given up to an exponent which is approximated by the experimentally decided density parameters of dark matter and...

We make a comparison for ten typical, popular darkenergy models according to theirs capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the darkenergy models. The generalized Chaplygin gas model, the constant $w$ model, and the $\\alpha$ darkenergy model are worse than the cosmological constant model, but still are good models compared to others. The holographic darkenergy model, the new generalized Chaply...

It has now been firmly established that the Universe is expanding at an accelerated rate, driven by a presently unknown form of darkenergy that appears to dominate our Universe today. A dedicated satellite mission has been designed to precisely map out the cosmological expansion history of the Universe and thereby determine the properties of the darkenergy. The SuperNova/Acceleration Probe (SNAP) will study thousands of distant supernovae, each with unprecedented precision, using a 2-meter aperture telescope with a wide field, large-area optical-to-near-IR imager and high-throughput spectrograph. SNAP can not only determine the amount of darkenergy with high precision, but test the nature of the darkenergy by examining how its equation of state evolves. The images produced by SNAP will have an unprecedented combination of depth, solid-angle, angular resolution, and temporal sampling and will provide a rich program of auxiliary science.

In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and darkenergy densities. We consider a number of different models (including the holographic darkenergy and darkenergy in a fractal universe) with interacting darkenergy (DE) and dark matter (DM), have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of darkenergy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a Universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model (SCM).

We simulate the density of darkenergy by using a power series to analyse the possible evolution of darkenergy. The parameters are constrained from the newly released Gold sample of the supernova dataset. The evolutions of darkenergy, as the power series from two free parameters to five free parameters, have the common and the different characters. We may conclude that either the density of darkenergy possibly oscillates or increases after it decreases to a minimum value. Accordingly, the state equation of darkenergy oscillates or evolves from ωde＞-1 in the past to ωde＜-1 around the present epoch.

Full Text Available In this article, we review a series of recent theoretical results regarding a conventional approach to the darkenergy (DE concept. This approach is distinguished among others for its simplicity and its physical relevance. By compromising General Relativity (GR and Thermodynamics at cosmological scale, we end up with a model without DE. Instead, the Universe we are proposing is filled with a perfect fluid of self-interacting dark matter (DM, the volume elements of which perform hydrodynamic flows. To the best of our knowledge, it is the first time in a cosmological framework that the energy of the cosmic fluid internal motions is also taken into account as a source of the universal gravitational field. As we demonstrate, this form of energy may compensate for the DE needed to compromise spatial flatness, while, depending on the particular type of thermodynamic processes occurring in the interior of the DM fluid (isothermal or polytropic, the Universe depicts itself as either decelerating or accelerating (respectively. In both cases, there is no disagreement between observations and the theoretical prediction of the distant supernovae (SNe Type Ia distribution. In fact, the cosmological model with matter content in the form of a thermodynamically-involved DM fluid not only interprets the observational data associated with the recent history of Universe expansion, but also confronts successfully with every major cosmological issue (such as the age and the coincidence problems. In this way, depending on the type of thermodynamic processes in it, such a model may serve either for a conventional DE cosmology or for a viable alternative one.

It may be difficult to single out the best model of darkenergy on the basis of the existing and planned cosmological observations, because many different models can lead to similar observational consequences. However, each particular model can be studied and either found consistent with observations or ruled out. In this paper, we concentrate on the possibility to test and rule out the simplest and by far the most popular of the models of darkenergy, the theory described by general relativity with positive vacuum energy (the cosmological constant). We evaluate the conditions under which this model could be ruled out by the future observations made by the Supernova/Acceleration Probe SNAP (both for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave background satellite.

It may be difficult to single out the best model of darkenergy on the basis of the existing and planned cosmological observations, because many different models can lead to similar observational consequences. However, each particular model can be studied and either found consistent with observations or ruled out. In this paper, we concentrate on the possibility to test and rule out the simplest and by far the most popular of the models of darkenergy, the theory described by general relativity with positive vacuum energy (the cosmological constant). We evaluate the conditions under which this model could be ruled out by the future observations made by the Supernova/Acceleration Probe SNAP (both for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave background satellite.

Dark matter is believed to be a major component of our universe. In this paper we propose a new mechanism based on dark matter inspired super-Chandrasekhar mass white dwarf to explain the recent observation of super luminous type Ia supernovae explosions. Our calculation shows when a white dwarf accretes enough dark matter, due to the Pauli exclusive principle between fermionic dark matter particles, the mass of corresponding dark white dwarf (which means the white dwarf mixed with dark matters) can significantly exceeds the Chandrasekhar limit. Moreover, we investigate some physical observable quantities, such as the redshift and moment of inertia of the dark white dwarf and found that these quantities are sensitive to the dark matter particle's distributions and thus can be potentially used to probe the relevant information of dark matter particles in the future.

We investigate a link between the running of the fine structure constant $\\alpha$ and a time evolving scalar darkenergy field. Employing a versatile parameterization for the equation of state, we exhaustively cover the space of darkenergy models. Under the assumption that the change in $\\alpha$ is to first order given by the evolution of the Quintessence field, we show that current Oklo, Quasi Stellar Objects and Equivalence Principle observations restrict the model parameters considerably stronger than observations of the Cosmic Microwave Background, Large Scale Structure and Supernovae Ia combined.

We investigate a link between the running of the fine structure constant α and a time evolving scalar darkenergy field. Employing a versatile parametrization for the equation of state, we exhaustively cover the space of darkenergy models. Under the assumption that the change in α is to first order given by the evolution of the quintessence field, we show that current Oklo, quasi-stellar object and equivalence principle observations restrict the model parameters considerably more strongly than observations of the cosmic microwave background, large scale structure and supernovae Ia combined.

We use the Markov ChainMonte Carlo method to investigate global constraints on the generalized holographic (GH) darkenergy with flat and non-flat universe from the current observed data: the Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. The most stringent constraints on the GH model parameter are obtained. In addition, it is found that the equation of state for this generalized holographic darkenergy can cross over the phantom boundary wde =-1.

We investigate how precisely we can determine the nature of darkenergy such as the equation of state (EoS) and its time dependence by using future observations of 21 cm fluctuations such as Square Kilometre Array (SKA) and Omniscope in combination with those from cosmic microwave background, baryon acoustic oscillation, type Ia supernovae and direct measurement of the Hubble constant. We consider several parametrizations for the EoS and find that future 21 cm observations will be powerful in constraining models of darkenergy, especially when its EoS varies at high redshifts.

The 2011 Nobel Prize for physics has been awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae", judged to be the "most important discovery or invention within the field of physics" (Excerpt from the will of Alfred Nobel). Are we forced by this claimed discovery to believe the universe is dominated by anti- gravitational darkenergy? Can the discovery be falsified? Because life as we observe it on Earth is virtually impossible by the standard ΛCDMHC model, extraterrestrial life and cometary panspermia may provide the first definitive falsification of a Nobel Prize in Physics since its first award in 1901 to Wilhelm Röntgen for his discovery of X-rays.

Full Text Available The Petrov classification of stress-energy tensors provides a model-independent definition of a vacuum by the algebraic structure of its stress-energy tensor and implies the existence of vacua whose symmetry is reduced as compared with the maximally symmetric de Sitter vacuum associated with the Einstein cosmological term. This allows to describe a vacuum in general setting by dynamical vacuum dark fluid, presented by a variable cosmological term with the reduced symmetry which makes vacuum fluid essentially anisotropic and allows it to be evolving and clustering. The relevant solutions to the Einstein equations describe regular cosmological models with time-evolving and spatially inhomogeneous vacuum darkenergy, and compact vacuum objects generically related to a darkenergy: regular black holes, their remnants and self-gravitating vacuum solitons with de Sitter vacuum interiors—which can be responsible for observational effects typically related to a dark matter. The mass of objects with de Sitter interior is generically related to vacuum darkenergy and to breaking of space-time symmetry. In the cosmological context spacetime symmetry provides a mechanism for relaxing cosmological constant to a needed non-zero value.

We propose and successfully test against new cosmological simulations a novel analytical description of the physical processes associated with the origin of cored dark matter density profiles. In the simulations, the potential in the central kiloparsec changes on sub-dynamical time-scales over the redshift interval 4 > z > 2, as repeated, energetic feedback generates large underdense bubbles of expanding gas from centrally concentrated bursts of star formation. The model demonstrates how fluctuations in the central potential irreversibly transfer energy into collisionless particles, thus generating a dark matter core. A supply of gas undergoing collapse and rapid expansion is therefore the essential ingredient. The framework, based on a novel impulsive approximation, breaks with the reliance on adiabatic approximations which are inappropriate in the rapidly changing limit. It shows that both outflows and galactic fountains can give rise to cusp flattening, even when only a few per cent of the baryons form stars. Dwarf galaxies maintain their core to the present time. The model suggests that constant density dark matter cores will be generated in systems of a wide mass range if central starbursts or active galactic nucleus phases are sufficiently frequent and energetic.

Edward Hubble in early 1900s observed red shifts for galaxies outside our solar system and found red shifts increasing linearly with distance. Modern telescopes looking at larger distances found a limit for use of red shift for extremely remote galaxies. Two ways of finding distances are (a) the light received (magnitude), and (b) the associated red shift. For very remote galaxies magnitude distances was larger than distances from red shift. Differences are wrongly explained by acceleration of receding velocities of these remote galaxies. DarkEnergy was used to supply acceleration energy. Red shift is due to an increase in wavelength of the light, plus reduced energy and frequency of photons. Photon energy approaches zero with distance and must approach zero asymptotically and never is negative. This explains differences between very large distances determined optically and by red shift. There is no acceleration - DarkEnergy is not needed. It is (wrongly) suggested that DarkEnergy adds to Dark Matter by Einstein's relation between energy and matter. We also question the use of red shift to show the expanding velocity through the Doppler effect [1]. [4pt] [1] The Misunderstood Universe, Aisenberg, S., (New York, 2009)

In order to make accurate measurements of darkenergy, a system is needed to monitor the focus and alignment of the DarkEnergy Camera (DECam) to be located on the Blanco 4m Telescope for the upcoming DarkEnergy Survey. One new approach under development is to fit out-of-focus star images to a point spread function from which information about the focus and tilt of the camera can be obtained. As a first test of a new algorithm using this idea, simulated star images produced from a model of DECam in the optics software Zemax were fitted. Then, real images from the Mosaic II imager currently installed on the Blanco telescope were used to investigate the algorithm's capabilities. A number of problems with the algorithm were found, and more work is needed to understand its limitations and improve its capabilities so it can reliably predict camera alignment and focus.

Coloured relics servived after hadronization might have given birth to dark matter and darkenergy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and darkenergy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.

This paper reviews the progress reported at this Royal Society Discussion Meeting and advertizes some possible future directions in our drive to understand dark matter and darkenergy. Additionally, a first attempt is made to place in context the exciting new results from the WMAP satellite, which were published shortly after this Meeting. In the first part of this review, pieces of observational evidence shown here that bear on the amounts of dark matter and darkenergy are reviewed. Subsequ...

Here we generalize ideas of unified Dark Matter DarkEnergy in the context of Two Measure Theories and of Dynamical space time Theories. In Two Measure Theories one uses metric independent volume elements and this allows to construct unified Dark Matter DarkEnergy, where the cosmological constant appears as an integration constant associated to the eq. of motion of the measure fields. The Dynamical space time Theories generalize the Two Measure Theories by introducing a vector field whose eq...

In this paper, we constrain darkenergy models using a compendium of observations at low redshifts. We consider the darkenergy as a barotropic fluid, with the equation of state a constant as well the case where darkenergy equation of state is a function of time. The observations considered here are Supernova Type Ia data, Baryonic Acoustic Oscillation data and Hubble parameter measurements. We compare constraints obtained from these data and also do a combined analysis. The combined observational constraints put strong limits on variation of darkenergyenergy density with redshift. For varying darkenergy models, the range of parameters preferred by the supernova type Ia data is in tension with the other low redshift distance measurements.

We study the backreaction of free quantum fields on a flat Robertson-Walker spacetime. Apart from renormalization freedom, the vacuum energy receives contributions from both the trace anomaly and the thermal nature of the quantum state. The former represents a dynamical realisation of darkenergy, while the latter mimics an effective dark matter component. The semiclassical dynamics yield two classes of asymptotically stable solutions. The first reproduces the concordance model in a suitable regime. The second lacks a classical counterpart, but is in excellent agreement with recent observations.

We study the backreaction of free quantum fields on a flat Robertson-Walker spacetime. Apart from renormalization freedom, the vacuum energy receives contributions from both the trace anomaly and the thermal nature of the quantum state. The former represents a dynamical realisation of darkenergy, while the latter mimics an effective dark matter component. The semiclassical dynamics yield two classes of asymptotically stable solutions. The first reproduces the CDM model in a suitable regime. The second lacks a classical counterpart, but is in excellent agreement with recent observations. (orig.)

We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energy-momentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter space-time, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary Robertson-Walker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed Robertson-Walker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on sub-Hubble scales as in standard cold dark matter scenarios.

We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energy-momentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter space-time, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as non-relativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary Robertson-Walker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed Robertson-Walker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on sub-Hubble scales as in standard cold dark matter scenarios.

Based on a new kind of complementary principle, we describe physics concerning the cosmological constant problem in the framework of effective field theory and suggest that a dominant part of darkenergy can originate from the zero point energy due to another graviton that performs a complementary role vis-a-vis the ordinary one and obtains a tiny mass through the coupling to the vacuum energy of matters.

We use 21 Hubble parameter versus redshift data points from Simon et al., Gaztanaga et al., Stern et al., and Moresco et al. to place constraints on model parameters of constant and time-evolving darkenergy cosmologies. The inclusion of the eight new measurements results in H(z) constraints more restrictive than those derived by Chen and Ratra. These constraints are now almost as restrictive as those that follow from current Type Ia supernova (SNIa) apparent magnitude versus redshift data, which now more carefully account for systematic uncertainties. This is a remarkable result. We emphasize, however, that SNIa data have been studied for a longer time than the H(z) data, possibly resulting in a better estimate of potential systematic errors in the SNIa case. A joint analysis of the H(z), baryon acoustic oscillation peak length scale, and SNIa data favors a spatially flat cosmological model currently dominated by a time-independent cosmological constant but does not exclude slowly evolving darkenergy.

The DarkEnergy Space Telescope (DESTINY) is an all-grism NIR 1.8-m survey camera optimized to return richly sampled Hubble diagrams of Type Ia and Type II supernovae (SN) over the redshift range 0.5 the Universe as a function of time, and characterizing the nature of the so-called ``darkenergy" component of the Universe. SN will be discovered by repeated imaging of a 7.5-sq.-deg. area located at the north ecliptic poles. Grism spectra with resolving power λ/Δλ = R˜75 will provide broad-band spectrophotometry, redshifts, SN classification, and valuable time-resolved diagnostic data for understanding the SN explosion physics. This methodology features only a single mode of operation with no time-critical interactions, a single detector technology, and a single instrument. Although grism spectroscopy is slow compared with SN detection in any single broad-band filter for photometry, or to conventional slit spectra for spectral diagnostics, the multiplex advantage of being able to observe a large field of view simultaneously over a full octave in wavelength makes this approach highly competitive.

We describe a mission concept for a 1.8-meter near-infrared (NIR) grism-mode space telescope optimized to return richly sampled Hubble diagrams of Type Ia and Type II supernovae (SNe) over the redshift range 0.5 the Universe as a function of time, and characterizing the nature of darkenergy. The central concept for our proposed DarkEnergy Space Telescope (DESTINY) is an all-grism NIR survey camera. SNe will be discovered by repeated imaging of an area located at the north ecliptic pole. Grism spectra with resolving power l/Dl = R * 100 will provide broad-band spectrophotometry, redshifts, SNe classification, as well as valuable time-resolved diagnostic data for understanding the SN explosion physics. Our approach features only a single mode of operation, a single detector technology, and a single instrument. Although grism spectroscopy is slow compared to SN detection in any single broad-band filter for photometry, or to conventional slit spectra for spectral diagnostics, the multiplex advantage of observing a large field-of-view over a full octave in wavelength simultaneously makes this approach highly competitive.

Constellation-X (Con-X) will carry out two powerful and independent sets of tests of darkenergy based on X-ray observations of galaxy clusters, providing comparable accuracy to other leading darkenergy probes. The first group of tests will measure the absolute distances to clusters, primarily using measurements of the X-ray gas mass fraction in the largest, dynamically relaxed clusters, but with additional constraining power provided by follow-up observations of the Sunyaev-Zel'dovich (SZ) effect. As with supernovae studies, such data determine the transformation between redshift and true distance, d(z), allowing cosmic acceleration to be measured directly. The second, independent group of tests will use the exquisite spectroscopic capabilities of Con-X to determine scaling relations between X-ray observables and mass. Together with forthcoming X-ray and SZ cluster surveys, these data will help to constrain the growth of structure, which is also a strong function of cosmological parameters.

Darkenergy and dark matter are the dominant sources in the evolution of the late universe. They are currently only indirectly detected via their gravitational effects, and there could be a coupling between them without violating observational constraints. We investigate the background dynamics when darkenergy is modelled as exponential quintessence, and is coupled to dark matter via simple models of energy exchange. We introduce a new form of dark sector coupling, which leads to a more complicated dynamical phase space and has a better physical motivation than previous mathematically similar couplings.

We propose a novel coupled darkenergy model which is assumed to occur as a q-deformed scalar field and investigate whether it will provide an expanding universe phase. We consider the q-deformed darkenergy as coupled to dark matter inhomogeneities. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions. The attractor solutions imply that the coupled q-deformed darkenergy model is consistent with the conventional dark ene...

@@ To model the observed Universe containing both darkenergy and dark matter, we study the effective Yang-Mills condensate model of darkenergy and add a non-relativistic matter component as the dark matter, which is generated out of the decaying darkenergy at a constant rate Г, a parameter of our model. For the Universe driven by these two components, the dynamic evolution still has asymptotic behaviour: the expansion of the Universe is accelerating with an asymptotically constant rate H, and the densities of both components approach to finite constant values. Moreover, ΩA≈ 0.7 for darkenergy and Ωm ≈ 0.3 for dark matter are achieved if the decay rate Г is chosen such that Г/H～ 1.

AGN jets carry helical magnetic fields, which can affect dark matter if the latter is axionic. This preliminary study shows that, in the presence of strong helical magnetic fields, the nature of the axionic condensate may change and become darkenergy. Such darkenergy may affect galaxy formation and galactic dynamics, so this possibility should not be ignored when considering axionic dark matter.

Cosmic surveys provide crucial information about high energy physics including strong evidence for darkenergy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of darkenergy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV c...

Cosmic surveys provide crucial information about high energy physics including strong evidence for darkenergy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of darkenergy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.

Cosmic surveys provide crucial information about high energy physics including strong evidence for darkenergy, dark matter, and inflation. Ongoing and upcoming surveys will start to identify the underlying physics of these new phenomena, including tight constraints on the equation of state of darkenergy, the viability of modified gravity, the existence of extra light species, the masses of the neutrinos, and the potential of the field that drove inflation. Even after the Stage IV experiments, DESI and LSST, complete their surveys, there will still be much information left in the sky. This additional information will enable us to understand the physics underlying the dark universe at an even deeper level and, in case Stage IV surveys find hints for physics beyond the current Standard Model of Cosmology, to revolutionize our current view of the universe. There are many ideas for how best to supplement and aid DESI and LSST in order to access some of this remaining information and how surveys beyond Stage IV can fully exploit this regime. These ideas flow to potential projects that could start construction in the 2020's.

We make a comparison for ten typical, popular darkenergy models according to their capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the darkenergy models. The generalized Chaplygin gas model, the constant w model, and the α darkenergy model are worse than the cosmological constant model, but still are good models compared to others. The holographic darkenergy model, the new generalized Chaplygin gas model, and the Chevalliear-Polarski-Linder model can still fit the current observations well, but from an economically feasible perspective, they are not so good. The new agegraphic darkenergy model, the Dvali-Gabadadze-Porrati model, and the Ricci darkenergy model are excluded by the current observations. (orig.)

We make a comparison for ten typical, popular darkenergy models according to their capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the darkenergy models. The generalized Chaplygin gas model, the constant w model, and the α darkenergy model are worse than the cosmological constant model, but still are good models compared to others. The holographic darkenergy model, the new generalized Chaplygin gas model, and the Chevalliear-Polarski-Linder model can still fit the current observations well, but from an economically feasible perspective, they are not so good. The new agegraphic darkenergy model, the Dvali-Gabadadze-Porrati model, and the Ricci darkenergy model are excluded by the current observations.

We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of darkenergy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM). The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. This interaction term describes an exchange of energy flow between the DE and DM within dark sector. To show how the method works we do the reconstruction of the interaction function expanding it in terms of only the first six Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming two models: (a) a DE equation of the state parameter w =-1 (an interacting cosmological constant), (b) a DE equation of the state parameter w = constant, and using the Union2 SNe Ia data set from "The Supernova Cosmology Project"...

Darkenergy can be studied by its influence on the expansion of the Universe. We investigate current constraints on early darkenergy (EDE) achievable by the combined observational data from type Ia supernovae (557), baryon acoustic oscillations, the current cosmic microwave background and the observed Hubble parameter. We find that combining these data sets provides powerful constraints on early darkenergy and the best fit values of the parameters in 68％ and 95％ confidencelevel regions are: Ωm0 = 0.2897+0.0149+0.0207 Ωe =0.0129+0.0272+0.0381 = 0.2897-0.0138-0.0194, = 0.0129-0.0129-0.0129, w0 = -1.04l5+0.0891+0.1182 and h = 0.6988+0.0059+0.0083- 1.04155-0.109-0.1604 , 0.6988-0.0058- 0.0081 .

The equation of state (EOS), $w(z)$, is the most important parameter of darkenergy. We reconstruct the evolution of this EOS in a model-independent way using the latest cosmic microwave background (CMB) data from Planck and other observations, such as type Ia supernovae (SNe Ia), the baryonic acoustic oscillation measurements (SDSS, 6dF, BOSS, and WiggleZ), and the Hubble parameter value $H(z)$. The results show that the EOS is consistent with the cosmological constant at the $2\\sigma$ confidence level, not preferring a dynamical darkenergy. The uncorrelated EOS of darkenergy constraints from Planck CMB data are much tighter than those from the WMAP 9-year CMB data.

We consider a model where both darkenergy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting darkenergy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the darkenergy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.

Full Text Available We propose a novel coupled darkenergy model which is assumed to occur as a q-deformed scalar field and investigate whether it will provide an expanding universe phase. We consider the q-deformed darkenergy as coupled to dark matter inhomogeneities. We perform the phase-space analysis of the model by numerical methods and find the late-time accelerated attractor solutions. The attractor solutions imply that the coupled q-deformed darkenergy model is consistent with the conventional darkenergy models satisfying an acceleration phase of universe. At the end, we compare the cosmological parameters of deformed and standard darkenergy models and interpret the implications.

Cosmic rays are charged relativistic particles that reach the Earth with extremely high energies, providing striking evidence of the existence of effective accelerators in the Universe. Below an energy around $\\sim 10^{17}$ eV cosmic rays are believed to be produced in the Milky Way while above that energy their origin is probably extragalactic. In the early '30s supernovae were already identified as possible sources for the Galactic component of cosmic rays. After the '70s this idea has gained more and more credibility thanks to the the development of the diffusive shock acceleration theory, which provides a robust theoretical framework for particle energization in astrophysical environments. Afterwards, mostly in recent years, much observational evidence has been gathered in support of this framework, converting a speculative idea in a real paradigm. In this Chapter the basic pillars of this paradigm will be illustrated. This includes the acceleration mechanism, the non linear effects produced by accelerate...

We apply a parametric reconstruction method to a homogeneous, isotropic and spatially flat Friedmann-Robertson-Walker (FRW) cosmological model filled of a fluid of darkenergy (DE) with constant equation of state (EOS) parameter interacting with dark matter (DM)\\@. The reconstruction method is based on expansions of the general interaction term and the relevant cosmological variables in terms of Chebyshev polynomials which form a complete set orthonormal functions. This interaction term describes an exchange of energy flow between the DE and DM within dark sector. To show how the method works we do the reconstruction of the interaction function expanding it in terms of only the first six Chebyshev polynomials and obtain the best estimation for the coefficients of the expansion assuming three models: (a) a DE equation of the state parameter w = −1 (an interacting cosmological Λ), (b) a DE equation of the state parameter w = constant with a dark matter density parameter fixed, (c) a DE equation of the state parameter w = constant with a free constant dark matter density parameter to be estimated, and using the Union2 SNe Ia data set from ''The Supernova Cosmology Project'' (SCP) composed by 557 type Ia supernovae. In both cases, the preliminary reconstruction shows that in the best scenario there exist the possibility of a crossing of the noninteracting line Q = 0 in the recent past within the 1σ and 2σ errors from positive values at early times to negative values at late times. This means that, in this reconstruction, there is an energy transfer from DE to DM at early times and an energy transfer from DM to DE at late times. We conclude that this fact is an indication of the possible existence of a crossing behavior in a general interaction coupling between dark components.

Cosmological observations have revealed the existence of a dark matter sector, which is commonly assumed to be made up of one particle species only. However, this sector might be more complicated than we currently believe: there might be more than one dark matter species (for example two components of cold dark matter or a mixture of hot and cold dark matter) and there may be new interactions between these particles. In this paper we study the possibility of multiple dark matter species and interactions mediated by a darkenergy field. We study both the background and the perturbation evolution in these scenarios. We find that the background evolution of a system of multiple dark matter particles (with constant couplings) mimics a single fluid with a time-varying coupling parameter. However, this is no longer true on the perturbative level. We study the case of attractive and repulsive forces as well as a mixture of cold and hot dark matter particles.

We find that current cosmic microwave background anisotropy data strongly constrain the mean spatial curvature of the Universe to be near zero, or, equivalently, the total energy density to be near critical-as predicted by inflation. This result is robust to editing of data sets, and variation of other cosmological parameters (totaling seven, including a cosmological constant). Other lines of argument indicate that the energy density of nonrelativistic matter is much less than critical. Together, these results are evidence, independent of supernovae data, for darkenergy in the Universe.

The 1998 discovery of what seems an acceleration of the cosmic expansion was made using type Ia supernovae and was later confirmed by other cosmological observations. It has made a huge impact on cosmology, prompting theoreticians to explain the observations and introducing the concept of darkenergy into modern physics. A vast literature on darkenergy and its alternatives has appeared since then, and this is the first comprehensive book devoted to the subject. This book is addressed to an advanced audience comprising graduate students and researchers in cosmology. Although it contains forty four fully solved problems and the first three chapters are rather introductory, they do not constitute a self-consistent course in cosmology and this book assumes graduate level knowledge of cosmology and general relativity. The fourth chapter focuses on observations, while the rest of this book addresses various classes of models proposed, including the cosmological constant, quintessence, k-essence, phantom energy, coupled darkenergy, etc. The title of this book should not induce the reader into believing that only darkenergy models are addressed—the authors devote two chapters to discussing conceptually very different approaches alternative to darkenergy, including ƒ(R) and Gauss-Bonnet gravity, braneworld and void models, and the backreaction of inhomogeneities on the cosmic dynamics. Two chapters contain a general discussion of non-linear cosmological perturbations and statistical methods widely applicable in cosmology. The final chapter outlines future perspectives and the most likely lines of observational research on darkenergy in the future. Overall, this book is carefully drafted, well presented, and does a good job of organizing the information available in the vast literature. The reader is pointed to the essential references and guided in a balanced way through the various proposals aimied at explaining the cosmological observations. Not all classes of

Maps of the Universe when it was 400,000 years old from observations of the cosmic microwave background and over the last ten billion years from galaxy surveys point to a compelling cosmological model. This model requires a very early epoch of accelerated expansion, inflation, during which the seeds of structure were planted via quantum mechanical fluctuations. These seeds began to grow via gravitational instability during the epoch in which dark matter dominated the energy density of the universe, transforming small perturbations laid down during inflation into nonlinear structures such as million light-year sized clusters, galaxies, stars, planets, and people. Over the past few billion years, we have entered a new phase, during which the expansion of the Universe is accelerating presumably driven by yet another substance, darkenergy.

We show that quantum decoherence, in the context of observational cosmology, can be connected to the cosmic darkenergy. The decoherence signature could be characterized by the existence of quantum entanglement between cosmological eras. As a consequence, the Von Neumann entropy related to the entanglement process, can be compared to the thermodynamical entropy in a homogeneous and isotropic universe. The corresponding cosmological models are compatible with the current observational bounds being able to reproduce viable equations of state without introducing {\\it a priori} any cosmological constant. In doing so, we investigate two cases, corresponding to two suitable cosmic volumes, $V\\propto a^3$ and $V\\propto H^{-3}$, and find two models which fairly well approximate the current cosmic speed up. The existence of darkenergy can be therefore reinterpreted as a quantum signature of entanglement, showing that the cosmological constant represents a limiting case of a more complicated model derived from the qua...

We perform a detailed investigation on the cosmological constraints on the holographic darkenergy (HDE) model by using the Plank data. We find that HDE can provide a good fit to the Plank high-l (l gtrsim 40) temperature power spectrum, while the discrepancy at l simeq 20-40 found in the ΛCDM model remains unsolved in the HDE model. The Plank data alone can lead to strong and reliable constraint on the HDE parameter c. At the 68% confidence level (CL), we obtain c = 0.508 ± 0.207 with Plank+WP+lensing, favoring the present phantom behavior of HDE at the more than 2σ CL. By combining Plank+WP with the external astrophysical data sets, i.e. the BAO measurements from 6dFGS+SDSS DR7(R)+BOSS DR9, the direct Hubble constant measurement result (H0 = 73.8 ± 2.4 kms-1Mpc-1) from the HST, the SNLS3 supernovae data set, and Union2.1 supernovae data set, we get the 68% CL constraint results c = 0.484 ± 0.070, 0.474 ± 0.049, 0.594 ± 0.051, and 0.642 ± 0.066, respectively. The constraints can be improved by 2%-15% if we further add the Plank lensing data into the analysis. Compared with the WMAP-9 results, the Plank results reduce the error by 30%-60%, and prefer a phantom-like HDE at higher significant level. We also investigate the tension between different data sets. We find no evident tension when we combine Plank data with BAO and HST. Especially, we find that the strong correlation between Ωmh3 and darkenergy parameters is helpful in relieving the tension between the Plank and HST measurements. The residual value of χ2Plank+WP+HST-χ2Plank+WP is 7.8 in the ΛCDM model, and is reduced to 1.0 or 0.3 if we switch the darkenergy to w model or the holographic model. When we introduce supernovae data sets into the analysis, some tension appears. We find that the SNLS3 data set is in tension with all other data sets; for example, for the Plank+WP, WMAP-9 and BAO+HST, the corresponding Δχ2 is equal to 6.4, 3.5 and 4.1, respectively. As a comparison, the Union2

Taking into account the experimental results of the HiRes and AUGER collaborations, the present status of bounds on Lorentz symmetry violation (LSV) patterns is discussed. Although significant constraints will emerge, a wide range of models and values of parameters will still be left open. Cosmological implications of allowed LSV patterns are discussed focusing on the origin of our Universe, the cosmological constant, dark matter and darkenergy. Superbradyons (superluminal preons) may be the actual constituents of vacuum and of standard particles, and form equally a cosmological sea leading to new forms of dark matter and darkenergy.

"The mysterious increase in the acceleration of the universe, when intuition says it should be slowing down, is postulated to be caused by darkenergy - "dark" because it is undetected. Now a group of scientists in the international collaboration Essence has suggested that a quantum mechanical interpretation of Einstein's proposed "cosmological constant" is the simplest explanation for darkenergy. The group measured darkenergy to within 10 percent." (1,5 page)

The possibility of strange stars mixed with darkenergy to be one of candidates for darkenergy stars is the main issue of the present study. Our investigation shows that quark matter is acting as darkenergy after certain yet unknown critical condition inside the quark stars. Our proposed model reveals that strange stars mixed with darkenergy feature not only a physically acceptable stable model but also mimic characteristics of darkenergy stars. The plausible connections are shown through the mass-radius relation as well as the entropy and temperature. We particulary note that two-fluid distribution is the major reason for anisotropic nature of the spherical stellar system.

We introduce an effective one-fluid description of the interacting dark sector in a spatially flat Friedmann-Robertson-Walker space-time and investigate the stability of the power-law solutions. We find the "source equation" for the total energy density and determine the energy density of each dark component. We study linear and nonlinear interactions which depend on the dark matter and darkenergy densities, their first derivatives, the total energy density with its derivatives up to second order and the scale factor. We solve the evolution equations of the dark components for both interactions, examine exhaustively several examples and show cases where the problem of the coincidence is alleviated. We show that a generic nonlinear interaction gives rise to the "relaxed Chaplygin gas model" whose effective equation of state includes the variable modified Chaplygin gas model while some others nonlinear interactions yield de Sitter and power-law scenarios.

Recent observations favour an accelerating Universe dominated by the darkenergy. We take the effective YangMills condensate as the darkenergy and couple it to a relativistic matter which is created by the decaying condensate. The dynamic evolution has asymptotic behaviour with finite constant energy densities, and the fractional densities Ω∧～ 0.7 for darkenergy and Ωm ～ 0.3 for relativistic matter are achieved at proper values of the decay rate. The resulting expansion of the Universe is in the de Sitter acceleration.

Recently, Kallosh and Linde have drawn attention to a new family of superconformal inflationary potentials, subsequently called $\\alpha$-attractors. The $\\alpha$-attractor family can interpolate between a large class of inflationary models. It also has an important theoretical underpinning within the framework of supergravity. We demonstrate that the $\\alpha$-attractors have an even wider appeal since they may describe dark matter and perhaps even darkenergy. The dark matter associated with ...

A cosmological model of darkenergy interacting with dark matter and another general component of the universe is investigated. We found general constraints on these models imposing an accelerated expansion. The same is also studied in the case for holographic darkenergy.

In present paper a spherically symmetric stellar configuration has been analyzed by assuming the matter distribution of the stellar configuration is anisotropic in nature and compared with the realistic objects, namely, the low mass X-ray binaries (LMXBs) and X-ray pulsars. The analytic solution has been obtained by utilizing the darkenergy equation of state for the interior solution corresponding to the Schwarzschild exterior vacuum solution at the junction interface. Several physical properties like energy conditions, stability, mass-radius ratio, and surface redshift are described through mathematical calculations as well as graphical plots. It is found that obtained mass-radius ration of the compact stars candidates like 4U 1820-30, PSR J 1614-2230, Vela X-1 and Cen X-3 are very much consistent with the observed data by Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431, 3216 (2013)). So our proposed model would be useful in the investigation of the possible clustering of darkenergy.

DarkEnergy is currently one of the biggest mysteries in science. In this article the origin of the concept is traced as far back as Newton and Hooke in the seventeenth century. Newton considered, along with the inverse square law, a force of attraction that varies linearly with distance. A direct link can be made between this term and Einstein's cosmological constant, Lambda, and this leads to a possible relation between Lambda and the total mass of the universe. Mach's influence on Einstein is discussed and the convoluted history of Lambda throughout the last ninety years is coherently presented.

Is DarkEnergy justified as an alternative to the cosmological constant $\\Lambda$ in order to explain the acceleration of the cosmic expansion ? It turns out that a straightforward dimensional analysis of Einstein equation provides us with clear evidences that the geometrical nature of $\\Lambda$ is the only viable source to this phenomenon, in addition of the application of Ockham's razor principle. This contribution is primarily a review of the main stream in the interpretation of $\\Lambda$ because it is at the origin of such a research program.

The nature of darkenergy, driving the accelerated expansion of the Universe, is one of the most important issues in modern astrophysics. In order to understand this phenomenon, we need precise astrophysical probes of the universal expansion spanning wide redshift ranges. Quasars have recently emerged as such a probe, thanks to their high intrinsic luminosities and, most importantly, our ability to measure their luminosity distances independently of redshifts. Here we report our ongoing work on observational reverberation mapping using the time delay of the Mg II line, performed with the South African Large Telescope (SALT).

We present and employ a new kinematical approach to cosmological ''darkenergy'' studies. We construct models in terms of the dimensionless second and third derivatives of the scale factor a(t) with respect to cosmic time t, namely the present-day value of the deceleration parameter q{sub 0} and the cosmic jerk parameter, j(t). An elegant feature of this parameterization is that all {Lambda}CDM models have j(t) = 1 (constant), which facilitates simple tests for departures from the {Lambda}CDM paradigm. Applying our model to the three best available sets of redshift-independent distance measurements, from type Ia supernovae and X-ray cluster gas mass fraction measurements, we obtain clear statistical evidence for a late time transition from a decelerating to an accelerating phase. For a flat model with constant jerk, j(t) = j, we measure q{sub 0} = -0.81 {+-} 0.14 and j = 2.16{sub -0.75}{sup +0.81}, results that are consistent with {Lambda}CDM at about the 1{sigma} confidence level. A standard ''dynamical'' analysis of the same data, employing the Friedmann equations and modeling the darkenergy as a fluid with an equation of state parameter, w (constant), gives {Omega}{sub m} = 0.306{sub -0.040}{sup +0.042} and w = -1.15{sub -0.18}{sup +0.14}, also consistent with {Lambda}CDM at about the 1{sigma} level. In comparison to dynamical analyses, the kinematical approach uses a different model set and employs a minimum of prior information, being independent of any particular gravity theory. The results obtained with this new approach therefore provide important additional information and we argue that both kinematical and dynamical techniques should be employed in future darkenergy studies, where possible. Our results provide further interesting support for the concordance {Lambda}CDM paradigm.

The nature of the supernova leading to the Crab Nebula has long been controversial because of the low energy that is present in the observed nebula. One possibility is that there is significant energy in extended fast material around the Crab but searches for such material have not led to detections. An electron capture supernova model can plausibly account for the low energy and the observed abundances in the Crab. Here, we examine the evolution of the Crab pulsar wind nebula inside a freely expanding supernova and find that the observed properties are most consistent with a low energy event. Both the velocity and radius of the shell material, and the amount of gas swept up by the pulsar wind point to a low explosion energy (∼10{sup 50} erg). We do not favor a model in which circumstellar interaction powers the supernova luminosity near maximum light because the required mass would limit the freely expanding ejecta.

The nature of the supernova leading to the Crab Nebula has long been controversial because of the low energy that is present in the observed nebula. One possibility is that there is significant energy in extended fast material around the Crab but searches for such material have not led to detections. An electron capture supernova model can plausibly account for the low energy and the observed abundances in the Crab. Here, we examine the evolution of the Crab pulsar wind nebula inside a freely expanding supernova and find that the observed properties are most consistent with a low energy event. Both the velocity and radius of the shell material, and the amount of gas swept up by the pulsar wind point to a low explosion energy ($\\sim 10^{50}$ ergs). We do not favor a model in which circumstellar interaction powers the supernova luminosity near maximum light because the required mass would limit the freely expanding ejecta.

We use 21 Hubble parameter versus redshift data points, from Gazta\\~{n}aga et al. (2009), Stern et al. (2010), and Moresco et al. (2012), to place constraints on model parameters of constant and time-evolving darkenergy cosmologies. This is the largest set of H(z) data considered to date. The inclusion of the 8 new Moresco et al. (2012) measurements results in H(z) constraints more restrictive than those derived by Chen & Ratra (2011b). These constraints are now almost as restrictive as those that follow from current Type Ia supernova (SNIa) apparent magnitude versus redshift data (Suzuki et al. 2012), which now more carefully account for systematic uncertainties. This is a remarkable result. We emphasize however that SNIa data have been studied for a longer time than the H(z) data, possibly resulting in a better estimate of potential systematic errors in the SNIa case. A joint analysis of the H(z), baryon acoustic oscillation peak length scale, and SNIa data favors a spatially-flat cosmological model cu...

ability of X-ray observations to detect and study the hot gas in galaxy clusters. From these data, the ratio of the mass of the hot gas and the mass of the dark matter in a cluster can be determined. The observed values of the gas fraction depend on the assumed distance to the cluster, which in turn depends on the curvature of space and the amount of darkenergy in the universe. Galaxy Cluster Animation Galaxy Cluster Animation Because galaxy clusters are so large, they are thought to represent a fair sample of the matter content in the universe. If so, then relative amounts of hot gas and dark matter should be the same for every cluster. Using this assumption, Allen and colleagues adjusted the distance scale to determine which one fit the data best. These distances show that the expansion of the Universe was first decelerating and then began to accelerate about six billion years ago. Chandra's observations agree with supernova results including those from the Hubble Space Telescope (HST), which first showed darkenergy's effect on the acceleration of the Universe. Chandra's results are completely independent of the supernova technique - both in wavelength and the objects observed. Such independent verification is a cornerstone of science. In this case it helps to dispel any remaining doubts that the supernova technique is flawed. "Our Chandra method has nothing to do with other techniques, so they're definitely not comparing notes, so to speak," said Robert Schmidt of University of Potsdam in Germany, another coauthor on the study. Energy Distribution of the Universe Energy Distribution of the Universe Better limits on the amount of darkenergy and how it varies with time are obtained by combining the X-ray results with data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), which used observations of the cosmic microwave background radiation to discover evidence for darkenergy in the very early Universe. Using the combined data, Allen and his colleagues found

We discuss how to formulate a quantum field theory of darkenergy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of darkenergy are strongly constrained. Quintessence-generated long-range forces and radiative stability of the quintessence potential require that such dark matter and darkenergy are completely decoupled. However, if darkenergy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory. Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations.

We discuss how to formulate a quantum field theory of darkenergy interacting with dark matter. We show that the proposals based on the assumption that dark matter is made up of heavy particles with masses which are very sensitive to the value of darkenergy are strongly constrained. Quintessence-generated long range forces and radiative stability of the quintessence potential require that such dark matter and darkenergy are completely decoupled. However, if darkenergy and a fraction of dark matter are very light axions, they can have significant mixings which are radiatively stable and perfectly consistent with quantum field theory. Such models can naturally occur in multi-axion realizations of monodromies. The mixings yield interesting signatures which are observable and are within current cosmological limits but could be constrained further by future observations.

The dark sector of the Universe need not be completely separable into distinct dark matter and darkenergy components. We consider a model of early darkenergy in which the darkenergy mimics a dark matter component in both evolution and perturbations at early times. Barotropic aether darkenergy scales as a fixed fraction, possibly greater than one, of the dark matter density and has vanishing sound speed at early times before undergoing a transition. This gives signatures not only in cosmic expansion but in sound speed and inhomogeneities, and in number of effective neutrino species. Model parameters describe the timing, sharpness of the transition, and the relative abundance at early times. Upon comparison with current data, we find viable regimes in which the darkenergy behaves like dark matter at early times: for transitions well before recombination the darkenergy to dark matter fraction can equal or exceed unity, while for transitions near recombination the ratio can only be a few percent. After the ...

Darkenergy is some of the weirdest and most mysterious stuff in the universe that tends to increase the rate of expansion of the universe. Two commonly known forms of darkenergy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli whose energy density can vary with time. We explore one particular model for dynamic darkenergy: quintessence driven by a scalar dilaton field. We propose an ansatz for the form of the dilaton field, |ϕ(a)|mP ≡ α1 ln t + α2tn = α ln a + βa2ζ, where a is the scale factor and α and ζ are parameters of the model. This phenomenological ansatz for ϕ can be motivated by generic solutions of a scalar dilaton field in many effective string theory and string-inspired gravity models in four dimensions. Most of the earlier discussions in the literature correspond to the choice that ζ = 0 so that ϕ(t) ∝ ln t or ϕ(t) ∝ ln a(t). Using a compilation of current data including type Ia supernovae, we impose observational constraints on the slope parameters like α and ζ and then discuss the relation of our results to analytical constraints on various cosmological parameters, including the darkenergy equation of state. Some useful constraints are imposed on model parameters like α and ζ as well as on the darkenergy/dark matter couplings using results from structure formation. The constraints of this model are shown to encompass the cosmological constant limit within 1σ error bars.

This work provides the current theory and observations behind the cosmological phenomenon of darkenergy. The approach is comprehensivewith rigorous mathematical theory and relevant astronomical observations discussed in context.The book treats the background and history starting with the new-found importance of Einstein's cosmological constant (proposed long ago for the opposite purpose) in darkenergy formulation, as well as the frontiers of darkenergy.

Full Text Available We consider a tachyon scalar field which is nonminimally coupled to gravity in the framework of teleparallel gravity. We analyze the phase-space of the model, known as tachyonic teleparallel darkenergy, in the presence of an interaction between darkenergy and background matter. We find that although there exist some late-time accelerated attractor solutions, there is no scaling attractor. So, unfortunately interacting tachyonic teleparallel darkenergy cannot alleviate the coincidence problem.

We present a phenomenological interaction with a scale factor power law form which leads to the appearance of two kinds of perturbed terms, a scale factor spatial variation along with perturbed Hubble expansion rate. We study both the background and the perturbation evolution within the parametrized post-Friedmann scheme, obtaining that the exchange of energy-momentum can flow from darkenergy to dark matter in order to keep darkenergy and dark matter densities well defined at all times. We combine several measures of the cosmic microwave background (WMAP9+Planck) data, baryon acoustic oscillation measurements, redshift-space distortion data, JLA sample of supernovae, and Hubble constant for constraining the coupling constant and the exponent provided both parametrized the interaction itself. The joint analysis of ${\\rm Planck+WMAP9+BAO}$ ${\\rm +RSD+JLA+HST}$ data seems to favor large coupling constant, $\\xi_c = 0.34403427_{- 0.18907353}^{+ 0.14430125}$ at 1 $\\sigma$ level, and prefers a power law interactio...

The main goal of modern cosmology remains to summon up a self consistent policy, able to explain, in the framework of the Einstein's theory, the cosmic speed up and the presence of Dark Matter in the Universe. Accordingly to the Holographic principle, which postulates the existence of a minimal size of a physical region, we argue, in this paper, that if this size exists for the Universe and it is accrued from the independent geometrical second order invariants, it would be possible to ensure a surprising source for Dark Matter and a viable candidate for explaining the late acceleration of the Universe. Along the work, we develop low redshift tests, such as Supernovae Ia and kinematical analysis complied by the use of Cosmography and we compare the outcomes with higher redshift tests, such as CMB peak and anisotropy of the cosmic power spectrum. All the upshots are in agreement with the chance that our overture would be undertaken to be an unified one, being able as well to explain both the Dark Matter and Dar...

Recently, a model of modified gravity plus single scalar field model was proposed, in which the scalar couples both to the standard Riemannian volume form given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume form given in terms of an auxiliary maximal rank antisymmetric tensor gauge field. This model provides an exact unified description of both darkenergy (via dynamically generated cosmological constant) and dark matter (as a "dust" fluid due to a hidden nonlinear Noether symmetry). In this paper we test the model against Supernovae type Ia experimental data and investigate the future Universe evolution which follows from it. Our results show that this model has very interesting features allowing various scenarios of Universe evolution and in the same time perfectly fits contemporary observational data. It can describe exponentially expanding or finite expanding Universe and moreover, a Universe with phase transition of first kind. The phase trans...

The brane-world model proposed by Dvali, Gabadadze and Porrati (DGP) leads to an accelerated universe without cosmological constant or other form of darkenergy for the positive branch (element of = +1). For the negative branch (element of = -1) we have investigated the behavior of a model with an holographic Ricci-like darkenergy and dark matter, where the IR cutoff takes the form αH{sup 2} + βH, H being the Hubble parameter and α, β positive constants of the model. We perform an analytical study of the model in the late-time darkenergy dominated epoch, where we obtain a solution for r{sub c}H(z), where r{sub c} is the leakage scale of gravity into the bulk, and conditions for the negative branch on the holographic parameters α and β, in order to hold the conditions of weak energy and accelerated universe. On the other hand, we compare the model versus the late-time cosmological data using the latest type Ia supernova sample of the Joint Light-curve Analysis (JLA), in order to constrain the holographic parameters in the negative branch, as well as r{sub c}H{sub 0} in the positive branch, where H{sub 0} is the Hubble constant. We find that the model has a good fit to the data and that the most likely values for (r{sub c}H{sub 0}, α, β) lie in the permitted region found from an analytical solution in a darkenergy dominated universe. We give a justification to use a holographic cutoff in 4D for the darkenergy in the 5-dimensional DGP model. Finally, using the Bayesian Information Criterion we find that this model is disfavored compared with the flat ΛCDM model. (orig.)

The authors present measurements of the angular cross-correlation between luminous red galaxies from the Sloan Digital Sky Survey and the cosmic microwave background temperature maps from the Wilkinson Microwave Anisotropy Probe. They find a statistically significant achromatic positive correlation between these two data sets, which is consistent with the expected signal from the late Integrated Sachs-Wolfe (ISW) effect. they do not detect any anti-correlation on small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ) effect, although they do see evidence for some SZ effect for their highest redshift samples. Assuming a flat universe, their preliminary detection of the ISW effect provides independent physical evidence for the existence of darkenergy.

Assuming the form of the entropic darkenergy as arises form the surface term in the Einstein-Hilbert's action, it's evolution were analyzed in an expanding flat universe. The model parameters were evaluated by constraining model using the Union data on Type Ia supernovae. We found that the model predicts an early decelerated phase and a later accelerated phase at the background level. The evolution of the Hubble parameter, darkenergy density, equation of state parameter and deceleration parameter were obtained. The model is diagnosed with $Om$ parameter. The model is hardly seems to be supporting the linear perturbation growth for the structure formation. We also found that the entropic darkenergy shows phantom nature for redshifts $z<0.257.$ During the phantom epoch, the model predicts big-rip effect at which both the scale factor of expansion and the darkenergy density become infinitely large and the big rip time is found to be around 36 Giga Years from now.

This paper describes the response of the IceCube neutrino telescope located at the geographic south pole to outbursts of MeV neutrinos from the core collapse of nearby massive stars. IceCube was completed in December 2010 forming a lattice of 5160 photomultiplier tubes that monitor a volume of ~1 km3 in the deep Antarctic ice for particle induced photons. The telescope was designed to detect neutrinos with energies greater than 100 GeV. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low. Hence IceCube can also detect large numbers of MeV neutrinos by observing a collective rise in all photomultiplier rates on top of the dark noise. With 2 ms timing resolution, IceCube can detect subtle features in the temporal development of the supernova neutrino burst. For a supernova at the galactic center, its sensitivity matches that of a background-free megaton-scale supernova search experiment. The sensitivity decreases to 20 standard deviations at the galactic edge (30 kpc) and 6 standard deviations at the Large Magellanic Cloud (50 kpc). IceCube is sending triggers from potential supernovae to the Supernova Early Warning System. The sensitivity to neutrino properties such as the neutrino hierarchy is discussed, as well as the possibility to detect the neutronization burst, a short outbreak of \\barνe's released by electron capture on protons soon after collapse. Tantalizing signatures, such as the formation of a quark star or a black hole as well as the characteristics of shock waves, are investigated to illustrate IceCube's capability for supernova detection.

In this work we construct a unified model of darkenergy and dark matter. This is done with the following three elements: a gravitating scalar field, φ with a non-conventional kinetic term, as in the string theory tachyon; an arbitrary potential, V(φ); two measures — a metric measure ((−g){sup 1/2}) and a non-metric measure (Φ). The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar field. (ii) The form of the darkenergy and dark matter that results from this model is fairly insensitive to the exact form of the scalar field potential.

Cosmological runaway solutions may exhibit an exact dilatation symmetry in the asymptotic limit of infinite time. In this limit, the massless dilaton or cosmon could be accompanied by another massless scalar field - the geon. At finite time, small time-dependent masses for both the cosmon and geon are still present due to imperfect dilatation symmetry. For a sufficiently large mass the geon will start oscillating and play the role of dark matter, while the cosmon is responsible for darkenergy. The common origin of the mass of both fields leads to an effective interaction between dark matter and darkenergy. Realistic cosmologies are possible for a simple form of the effective cosmon-geon-potential. We find an inverse geon mass of a size where it could reduce subgalactic structure formation.

For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.

The standard model of cosmology considers the existence of two components of unknown nature, ``dark matter'' and ``darkenergy'', which determine the cosmological evolution. Their nature remains unknown, and other models can also be considered. In particular, it may be possible to reinterpret the recent cosmological observations so that the Universe does not contain two fluids of unknown natures, but only one fluid with particular properties. After a brief review of constraints on this unifyi...

Dark matter and darkenergy are usually assumed to be independent, coupling only gravitationally. An extension to this simple picture is to model darkenergy as a scalar field which is directly coupled to the cold dark matter fluid. Such a non-trivial coupling in the dark sector leads to a fifth force and a time-dependent dark matter particle mass. In this work we examine the impact that darkenergy-dark matter couplings have on weak lensing statistics by constructing realistic simulated weak-lensing maps using raytracing techniques through a suite of N-body cosmological simulations. We construct maps for an array of different lensing quantities, covering a range of scales from a few arcminutes to several degrees. The concordance $\\Lambda$CDM model is compared to different coupled darkenergy models, described either by an exponential scalar field potential (standard coupled darkenergy scenario) or by a SUGRA potential (bouncing model). We analyse several statistical quantities, in particular the power spect...

In this paper we present an exact solution of Einstein's field equations describing the Schwarzschild black hole in darkenergy background. It is also regarded as an embedded solution that the Schwarzschild black hole is embedded into the darkenergy space producing Schwarzschild-darkenergy black hole. It is found that the space-time geometry of Schwarzschild-darkenergy solution is non-vacuum Petrov type $D$ in the classification of space-times. We study the energy conditions (like weak, strong and dominant conditions) for the energy-momentum tensor of the Schwarzschild-darkenergy solution. We also find that the energy-momentum tensor of the Schwarzschild-darkenergy solution violates the strong energy condition due to the negative pressure leading to a repulsive gravitational force of the matter field in the space-time. It is shown that the time-like vector field for an observer in the Schwarzschild-darkenergy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity...

Darkenergy is one of the mysteries of the twenty first century. Although there are candidates resembling some features of darkenergy, there is no single model describing all the properties of darkenergy. Darkenergy is believed to be the most dominant component of the cosmic inventory, but a lot of models do not consider any interaction between darkenergy and other constituents of the cosmic inventory. Introducing an interaction will change the equation governing the behavior of darkenergy and matter and creates new ways to explain cosmic coincidence problem. In this work we studied how the Hubble parameter and density parameters evolve with time in the presence of certain types of interaction. The interaction serves as a way to convert darkenergy into matter to avoid a darkenergy-dominated universe by creating new equilibrium points for the differential equations. Then we will use numerical analysis to predict the values of distance moduli at different redshifts and compare them to the values for the distance moduli obtained by WMAP (Wilkinson Microwave Anisotropy Probe). Undergraduate Student

Time is a parameter playing a central role in our most fundamental modelling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative motions and on the strength of the gravitational field in which they are embedded. In standard cosmology, the time parameter is the one measured by fundamental clocks, i.e. clocks at rest with respect to the expanding space. This proper time is assumed to flow at a constant rate throughout the whole history of the Universe. We make the alternative hypothesis that the rate at which cosmological time flows depends on the global geometric curvature the Universe. Using a simple one-parameter model for the relation between proper time and curvature, we build a cosmological model that fits the Type Ia Supernovae data (the best cosmological standard candles) without the need for darkenergy nor probably exotic dark matter.

It is shown that the vacuum condensate induced by many phenomena behaves as a perfect fluid which, under particular conditions, has zero or negative pressure. In particular, the condensates of thermal states, of fields in curved space and of mixed particles have been analyzed. It is shown that the thermal states with the cosmic microwave radiation temperature, the Unruh and the Hawking radiations give negligible contributions to the critical energy density of the universe, while the thermal vacuum of the intercluster medium could contribute to the dark matter, together with the vacuum energy of fields in curved space-time and of mixed neutrinos. Moreover, a component of the darkenergy can be represented by the vacuum of axion-like particles mixed with photons and superpartners of neutrinos. The formal analogy among the systems characterized by the condensates can open new scenarios in the possibility to detect the dark components of the universe in table top experiments.

Full Text Available It is shown that the vacuum condensate induced by many phenomena behaves as a perfect fluid which, under particular conditions, has zero or negative pressure. In particular, the condensates of thermal states of fields in curved space and of mixed particles have been analyzed. It is shown that the thermal states with the cosmic microwave radiation temperature and the Unruh and the Hawking radiations give negligible contributions to the critical energy density of the universe, while the thermal vacuum of the intercluster medium could contribute to the dark matter, together with the vacuum energy of fields in curved space-time and of mixed neutrinos. Moreover, a component of the darkenergy can be represented by the vacuum of axion-like particles mixed with photons and superpartners of neutrinos. The formal analogy among the systems characterized by the condensates can open new scenarios in the possibility of detecting the dark components of the universe in table top experiments.

We review the evidence for recently accelerating cosmological expansion or ''darkenergy'', either a negative pressure constituent in General Relativity (DarkEnergy) or modified gravity (Dark Gravity), without any constituent DarkEnergy. If constituent DarkEnergy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of ''darkenergy'' cannot be derived from the homogeneous expansion history alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, but also allow nearly static DarkEnergy or gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish between static and ''dynamic'' ''darkenergy''. But, cosmologically distinguishing the Concordance Model {lambda}CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati low-curvature modifications of Einstein gravity may also be detected in refined observations in the solar system (Lue and Starkman) or at the intermediate Vainstein scale (Iorio) in isolated galaxy clusters. DarkEnergy's epicyclic character, failure to explain the original Cosmic Coincidence (''Why so small now?'') without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity. (Orig.)

In this paper we consider a correspondence between the holographic darkenergy density and tachyon energy density in FRW universe. Then we reconstruct the potential and the dynamics of the tachyon field which describe tachyon cosmology.

The DarkEnergy Survey (DES) is an operating optical survey aimed at understanding the accelerating expansion of the universe using four complementary methods: weak gravitational lensing, galaxy cluster counts, baryon acoustic oscillations, and Type Ia supernovae. To perform the 5000 sq-degree wide field and 30 sq-degree supernova surveys, the DES Collaboration built the DarkEnergy Camera (DECam), a 3 square-degree, 570-Megapixel CCD camera that was installed at the prime focus of the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO). DES has completed its third observing season out of a nominal five. This paper describes DES “Year 1” (Y1) to “Year 3” (Y3), the strategy, an outline of the survey operations procedures, the efficiency of operations and the causes of lost observing time. It provides details about the quality of the first three season's data, and describes how we are adjusting the survey strategy in the face of the El Niño Southern Oscillation

Full Text Available We review matter bounce scenarios where the matter content is dark matter and darkenergy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence, could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.

We review matter bounce scenarios where the matter content is dark matter and darkenergy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.

We review matter bounce scenarios where the matter content is dark matter and darkenergy. These cosmologies predict a nearly scale-invariant power spectrum with a slightly red tilt for scalar perturbations and a small tensor-to-scalar ratio. Importantly, these models predict a positive running of the scalar index, contrary to the predictions of the simplest inflationary and ekpyrotic models, and hence could potentially be falsified by future observations. We also review how bouncing cosmological space-times can arise in theories where either the Einstein equations are modified or where matter fields that violate the null energy condition are included.

The rate of structure formation in the Universe is different in homogeneous and clustered darkenergy models. The degree of darkenergy clustering depends on the magnitude of its effective sound speed $c^{2}_{\\rm eff}$ and for $c_{\\rm eff}=0$ darkenergy clusters in a similar fashion to dark matter while for $c_{\\rm eff}=1$ it stays (approximately) homogeneous. In this paper we consider two distinct equations of state for the darkenergy component, $w_{\\rm d}=const$ and $w_{\\rm d}=w_0+w_1\\left(\\frac{z}{1+z}\\right)$ with $c_{\\rm eff}$ as a free parameter and we try to constrain the darkenergy effective sound speed using current available data including SnIa, Baryon Acoustic Oscillation, CMB shift parameter ({\\em Planck} and {\\em WMAP}), Hubble parameter, Big Bang Nucleosynthesis and the growth rate of structures $f\\sigma_{8}(z)$. At first we derive the most general form of the equations governing dark matter and darkenergy clustering under the assumption that $c_{\\rm eff}=const$. Finally we constrain the mod...

A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic (p\\sim -rho), very smooth form of energy called ``darkenergy'' accounting for about 75% of the Universe. The ``simplest'' explanation for darkenergy is the zero-point energy density associated with the quantum vacuum; however, all estimates for its value are many orders-of-magnitude too large. Other ideas for darkenergy include a very light scalar field or a tangled network of topological defects. An alternate explanation invokes gravitational physics beyond general relativity. Observations and experiments underway and more precise cosmological measurements and laboratory experiments planned for the next decade will test whether or not darkenergy is the quantum energy of the vacuum or something more exotic, and whether or not general relati...

The Hubble relation between distance and redshift is a purely cosmographic relation that depends only on the symmetries of a FLRW spacetime, but does not intrinsically make any dynamical assumptions. This suggests that it should be possible to estimate the parameters defining the Hubble relation without making any dynamical assumptions. To test this idea, we perform a number of inter-related cosmographic fits to the legacy05 and gold06 supernova datasets, paying careful attention to the systematic uncertainties. Based on this supernova data, the "preponderance of evidence" certainly suggests an accelerating universe. However we would argue that (unless one uses additional dynamical and observational information, and makes additional theoretical assumptions) this conclusion is not currently supported "beyond reasonable doubt". As part of the analysis we develop two particularly transparent graphical representations of the redshift-distance relation -- representations in which acceleration versus deceleration r...

This document presents the results from the Distances subgroup of the Cosmic Frontier Community Planning Study (Snowmass 2013). We summarize the current state of the field as well as future prospects and challenges. In addition to the established probes using Type Ia supernovae and baryon acoustic oscillations, we also consider prospective methods based on clusters, active galactic nuclei, gravitational wave sirens and strong lensing time delays.

This document presents the results from the Distances subgroup of the Cosmic Frontier Community Planning Study (Snowmass 2013). We summarize the current state of the field as well as future prospects and challenges. In addition to the established probes using Type IA supernovae and baryon acoustic oscillations, we also consider prospective methods based on clusters, active galactic nuclei, gravitational wave sirens and strong lensing time delays.

The initial condition Ωde (zini) =n2(1 + Zini)-2/4 at Zini =2000,widely used to solve the differential equation of the density of the new agegraphic darkenergy (NADE) Ωde,makes the NADE model a single-parameter dark-energy cosmological model.However,we find that this initial condition is only applicable in a fiat universe with only darkenergy and pressureless matter.In fact,in order to obtain more information from current observational data,such as the cosmic microwave background (CMB) and the baryon acoustic oscillations (BAO),we need to consider the contribution of radiation.For this situation,the initial condition mentioned above becomes invalid.To overcome this shortcoming,we investigate the evolutions of darkenergy in matter-dominated and radiation-dominated epochs,and obtain a new initial condition Ωde(Zini) =n2(1 + zini)-2(1+ √F(Zini))2/4 at zini =2000,where F(z) ≡ Ωr0(1+z)/[Ωm0 + Ωr0(1 +z)] with Ωr0 and Ωm0 being the current density parameters of radiation and pressureless matter,respectively.This revised initial condition is applicable for the differential equation of Ωde obtained in the standard Friedmann-Robertson-Walker (FRW) universe with darkenergy,pressureless matter,radiation,and even spatial curvature,and can still keep the NADE model as a single-parameter model.With the revised initial condition and the observational data of type Ia supernova (SNIa),CMB,and BAO,we finally constrain the NADE model.The results show that the single free parameter n of the NADE model can be constrained tightly.

Solutions to the energy-independent (gray) radiative transfer equations are compared to results of Monte Carlo simulations of the Ni-56 and Co-56 decay gamma-ray energy deposition in supernovae. The comparison shows that an effective, purely absorptive, gray opacity, kappa(sub gamma) approximately (0. 06 +/- 0.01)Y(sub e) sq cm/g, where Y is the total number of electrons per baryon, accurately describes the interaction of gamma-rays with the cool supernova gas and the local gamma-ray energy deposition within the gas. The nature of the gamma-ray interaction process (dominated by Compton scattering in the relativistic regime) creates a weak dependence of kappa(sub gamma) on the optical thickness of the (spherically symmetric) supernova atmosphere: The maximum value of kappa(sub gamma) applies during optically thick conditions when individual gamma-rays undergo multiple scattering encounters and the lower bound is reached at the phase characterized by a total Thomson optical depth to the center of the atmosphere tau(sub e) approximately less than 1. Gamma-ray deposition for Type Ia supernova models to within 10% for the epoch from maximum light to t = 1200 days. Our results quantitatively confirm that the quick and efficient solution to the gray transfer problem provides an accurate representation of gamma-ray energy deposition for a broad range of supernova conditions.

Bulk darkenergy properties are determined by the redshift evolution of its pressure-to-density ratio, $w_{de}(z)$. An experimental goal is to decide if the darkenergy is dynamical, as in the quintessence (and phantom) models treated here. We show that a three-parameter approximation $w_{de}(z; \\epsilon_s, \\epsilon_{\\phi\\infty}, \\zeta_s)$ fits well the ensemble of trajectories for a wide class of late-inflaton potentials $V(\\phi)$. Markov Chain Monte Carlo probability calculations are used to confront our $w_{de}(z)$ trajectories with current observational information on Type Ia supernova, Cosmic Microwave Background, galaxy power spectra, weak lensing and the Lyman-${\\alpha}$ forest. We find the best constrained parameter is a low redshift slope parameter, $\\epsilon_s \\propto (\\partial \\ln V / \\partial \\phi)^2$ when the darkenergy and matter have equal energy densities. A tracking parameter $\\epsilon_{\\phi\\infty}$ defining the high-redshift attractor of $1+w_{de}$ is marginally constrained. Poorly determin...

Darkenergy and cosmic acceleration is one of the three pillars of the current cosmological paradigm. Moreover, both raise fundamental issues in cosmology and particle physics. In particle physics, the darkenergy problem is intimately related to the perplexing issue of why the quantum energy of the vacuum is so small. In cosmology, the nature of the darkenergy is crucial to understanding the destiny of the Universe. I will discuss the status of current models for darkenergy -- including vacuum energy and rolling scalar fields -- their implications for cosmology and for particle physics and how they can be tested by WFIRST. I will also address the status of the possibility that cosmic acceleration is explained by modifying or replacing general relativity.

The book elucidates the current state of the darkenergy problem and presents the results of the authors, who work in this area. It describes the observational evidence for the existence of darkenergy, the methods and results of constraining of its parameters, modeling of darkenergy by scalar fields, the space-times with extra spatial dimensions, especially Kaluza---Klein models, the braneworld models with a single extra dimension as well as the problems of positive definition of gravitational energy in General Relativity, energy conditions and consequences of their violation in the presence of darkenergy. This monograph is intended for science professionals, educators and graduate students, specializing in general relativity, cosmology, field theory and particle physics.

The interpretation of a vast number of cosmological observations in the framework of FRW models suggests that the major part of the energy density of the universe is in form of darkenergy with still unknown physical nature. In some models for darkenergy, which are motivated by particle physics theory, the equation of state and the contribution of darkenergy to the energy density of the universe can be variable. Here we study structure formation in a parameterized darkenergy model, and compare its predictions with recent observational data, from the Supernova Ia gold sample and the parameters of large scale structure determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS), and put some constraints on the free parameters of this model.

The statefinder parameters ($r,s$) in two darkenergy models are studied. In the first, we discuss in four-dimensional General Relativity a two fluid model, in which darkenergy and dark matter are allowed to interact with each other. In the second model, we consider the DGP brane model generalized by taking a possible energy exchange between the brane and the bulk into account. We determine the values of the statefinder parameters that correspond to the unique attractor of the system at hand. Furthermore, we produce plots in which we show $s,r$ as functions of red-shift, and the ($s-r$) plane for each model.

It is argued that fluctuations of quantum fields in four-dimensional space do not give rise to darkenergy, but are rather a negligible contribution to dark matter. By (relativistic) dark matter we mean that the relation between pressure and energy density is $p=\\frac13 u$, while darkenergy is characterized by $p=-u$. A possible source of darkenergy are the fluctuations in quantum fields, including quantum gravity, inhabiting extra compactified dimensions. These fluctuations have been computed for some simple geometries, such as $S^2$, $S^4$, and $S^6$. If the extra dimensions are too small, they would give rise to a darkenergy larger than that observed, whereas if they are too large they would be in conflict with experimental tests of Newton's law. This notion suggests that the size of the extra dimensions is of order 100 $\\mu$m. If the limit on the size of extra dimensions becomes lower than this bound, extra dimensions probably do not exist, and another source for cosmological darkenergy will have to b...

Here we investigate the holographic darkenergy model in the framework of FRW cosmology where the Newtonian gravitational constant,$G$, is varying with cosmic time. Using the complementary astronomical data which support the time dependency of $G$, the evolutionary treatment of EoS parameter and energy density of darkenergy model are calculated in the presence of time variation of $G$. It has been shown that in this case, the phantom regime can be achieved at the present time. We also calculate the evolution of $G$- corrected deceleration parameter for holographic darkenergy model and show that the dependency of $G$ on the comic time can influence on the transition epoch from decelerated expansion to the accelerated phase. Finally we perform the statefinder analysis for $G$- corrected holographic model and show that this model has a shorter distance from the observational point in $s-r$ plane compare with original holographic darkenergy model.

Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and darkenergy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. Accordingly, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluid-like properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, the energy of this fluid's internal motions is also taken into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy needed to compromise spatial flatness, namely, to justify that, today, the total-energy density parameter is exactly unity. The poly...

We propose a new class of ``spintessence'' models for dark matter and/or negative-pressure, dynamical darkenergy consisting of a complex scalar field $\\phi$ spinning in a U(1)-symmetric potential $V(\\phi)=V(|\\phi|)$. As the Universe expands, the field spirals slowly toward the origin. The choice of $V(\\phi)$ determines the equation-of-state parameter ${w}$, which may be either constant or evolving with time. Spintessence models can introduce a variety of novel effects in the growth of density perturbations. We discuss connections with quintessence and self-interacting and fuzzy cold dark matter, possible implications for the coincidence problem, baryogenesis, and cosmological birefringence, as well as generalizations of spintessence to models with higher global symmetry and models in which the symmetry is not exact.

We show that the origin of the dark matter and darkenergy problems originates in the assumption of standard Einstein gravity that Newton's constant is fundamental. We discuss an alternate, conformal invariant, metric theory of gravity in which Newton's constant is induced dynamically, with the global induced one which is effective for cosmology being altogether weaker than the local induced one needed for the solar system. We find that in the theory dark matter is no longer needed, and that the accelerating universe data can be fitted without fine-tuning using a cosmological constant as large as particle physics suggests. In the conformal theory then it is not the cosmological constant which is quenched but rather the amount of gravity that it produces.

In this article, we review a series of recent theoretical results regarding a conventional approach to the darkenergy (DE) concept. This approach is distinguished among others for its simplicity and its physical relevance. By compromising General Relativity (GR) and Thermodynamics at cosmological scale, we end up with a model without DE. Instead, the Universe we are proposing is filled with a perfect fluid of self-interacting dark matter (DM), the volume elements of which perform hydrodynamic flows. To the best of our knowledge, it is the first time in a cosmological framework that the energy of the cosmic fluid internal motions is also taken into account as a source of the universal gravitational field. As we demonstrate, this form of energy may compensate for the DE needed to compromise spatial flatness, while, depending on the particular type of thermodynamic processes occurring in the interior of the DM fluid (isothermal or polytropic), the Universe depicts itself as either decelerating or accelerating (...

This paper describes the response of the IceCube neutrino telescope located at the geographic South Pole to outbursts of MeV neutrinos from the core collapse of nearby massive stars. IceCube was completed in December 2010 forming a lattice of 5160 photomultiplier tubes that monitor a volume of ~ 1 cubic kilometer in the deep Antarctic ice for particle induced photons. The telescope was designed to detect neutrinos with energies greater than 100 GeV. Owing to subfreezing ice temperatures, the photomultiplier dark noise rates are particularly low. Hence IceCube can also detect large numbers of MeV neutrinos by observing a collective rise in all photomultiplier rates on top of the dark noise. With 2 ms timing resolution, IceCube can detect subtle features in the temporal development of the supernova neutrino burst. For a supernova at the galactic center, its sensitivity matches that of a background-free megaton-scale supernova search experiment. The sensitivity decreases to 20 standard deviations at the galactic...

The discovery ten years ago that the expansion of the Universe is accelerating put in place the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% darkenergy. Yet the underlying cause of cosmic acceleration remains a mystery: it could arise from the repulsive gravity of darkenergy-for example, the quantum energy of the vacuum-or it may signal that General Relativity breaks down on cosmological scales and must be replaced. In these lectures, I present the observational evidence for cosmic acceleration and what it has revealed about darkenergy, discuss a few of the theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that we hope will shed light on this enigma in the coming years. Based on five lectures given at the XII Ciclo de Cursos Especiais at the Observatorio Nacional, Rio de Janeiro, Brazil, 1-5 October 2007.

The discovery ten years ago that the expansion of the Universe is accelerating put in place the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% darkenergy. Yet the underlying cause of cosmic acceleration remains a mystery: it could arise from the repulsive gravity of darkenergy -- for example, the quantum energy of the vacuum -- or it may signal that General Relativity breaks down on cosmological scales and must be replaced. In these lectures, I present the observational evidence for cosmic acceleration and what it has revealed about darkenergy, discuss a few of the theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that we hope will shed light on this enigma in the coming years.

"DOE and NASA announced their plan for a Joint DarkEnergy Mission (JDEM) on October 23, 2003, at the NASA Office of Space Science Structure and Evolution of the Universe Subcommittee (SEUS) meeting" (1 paragraph).

The braneworld model proposed by Dvali, Gabadadze, and Porrati leads to an accelerated universe without cosmological constant or any other form of darkenergy. Nevertheless, we have investigated the consequences of this model when an holographic darkenergy is included, taking the Hubble scale as IR cutoff. We have found that the holographic darkenergy leads to an accelerated flat universe (de Sitter-like expansion) for the two branches: {epsilon}={+-}1, of the DGP model. Nevertheless, in universes with no null curvature the darkenergy presents an EoS corresponding to a phantom fluid during the present era and evolving to a de Sitter-like phase for future cosmic time. In the special case in which the holographic parameter c is equal to one we have found a sudden singularity in closed universes. In this case the expansion is decelerating. (orig.)

A new gravitational model for darkenergy is presented based on the model of de Sitter gauge theory of gravity.In the model,in addition to the cosmological constant,the homogeneous and isotropic torsion and its coupling with curvature play an important role for darkenergy.The model may supply the universe with a natural transit from decelerating expansion to accelerating expansion.

Recent observations provide strong evidence that the universe is accelerating. This confronts theory with a severe challenge. Explanations of the acceleration within the framework of general relativity are plagued by difficulties. General relativistic models require a "darkenergy" field with effectively negative pressure. An alternative to darkenergy is that gravity itself may behave differently from general relativity on the largest scales, in such a way as to produce acceleration. The alt...

We investigate the phantom darkenergy model derived from the scalar field with a negative kinetic term. By assuming a particular relation between the time derivative of the phantom field and the Hubble function, an exact solution of the model is constructed. Absence of the 'big rip' singularity is shown explicitly. We then derive special features of phantom darkenergy model and show that its predictions are consistent with all astrophysical observations.

We present cosmological tests for a phenomenological parametrization of quintessence model with time-varying equation of state on low, intermediate and high redshift observations \\cite{w04}. We study the sensitivity of the comoving distance and volume element with the Alcock-Paczynski test to the time varying model of darkenergy. At the intermediate redshifts, Gold supernova Type Ia data is used to fit the quintessence model to the observed distance modulus. The value of the observed acoustic angular scale by WMAP experiment also is compared with the model. The combined result of CMB and SNIa data confines $w=p/\\rho$ to be more than -1.3 which can violate the dominant energy condition.

We investigate constraints on early darkenergy (EDE) from the Cosmic Microwave Background (CMB) anisotropy, taking into account data from WMAP9 combined with latest small scale measurements from the South Pole Telescope (SPT). For a constant EDE fraction we propose a new parametrization with one less parameter but still enough to provide similar results to the ones previously studied in literature. The main emphasis of our analysis, however, compares a new set of different EDE parametrizations that reveal how CMB constraints depend on the redshift epoch at which DarkEnergy was non negligible. We find that bounds on EDE get substantially weaker if darkenergy starts to be non-negligible later, with early darkenergy fraction Omega_e free to go up to about 5% at 2 sigma if the onset of EDE happens at z < 100. Tight bounds around 1-2% are obtained whenever darkenergy is present at last scattering, even if its effects switch off afterwards. We show that the CMB mainly constrains the presence of DarkEnergy ...

The present work deals with a kinematic approach to the modelling the late time dynamics of the universe. This approach is based upon the assumption of constant value of cosmological jerk parameter, which is the dimensionless representation of the 3rd order time derivative of the scale factor. For the $\\Lambda$CDM model, the value of jerk parameter is -1 throughout the evolution history. Now any model dependent estimation of the value of the jerk parameter would indicate the deviation of the model from the cosmological constant. In the present work, it has also been shown that for a constant jerk parameter model, any deviation of its value from -1 would not allow the dark matter to have an independent conservation, thus indicating towards an interaction between dark matter and darkenergy. Statistical analysis with different observational data sets (namely the observational Hubble parameter data (OHD), the type Ia supernova data (SNe), and the baryon acoustic oscillation data (BAO)) along with the cosmic micr...

The present work deals with a kinematic approach to modelling the late time dynamics of the universe. This approach is based upon the assumption of constant value of cosmological jerk parameter, which is the dimensionless representation of the third order time derivative of the scale factor. For the Λ CDM model, the value of jerk parameter is ‑1 throughout the evolution history. Now any model dependent estimation of the value of the jerk parameter would indicate the deviation of the model from the cosmological constant. In the present work, it has also been shown that for a constant jerk parameter model, any deviation of its value from ‑1 would not allow the dark matter to have an independent conservation, thus indicating an interaction between dark matter and darkenergy. Statistical analysis with different observational data sets (namely the observational Hubble parameter data (OHD), the type Ia supernova data (SNe), and the baryon acoustic oscillation data (BAO)) lead to well constrained values of the jerk parameter and the model remains at a very close proximity of the Λ CDM. The possibility of interaction is found to be more likely at high redshift rather than at the present epoch.

In this paper, we compare some popular darkenergy models with the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation, the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey and the Two Degree Field Galaxy Redshift Survey, and the cosmic microwave background measurement given by the five-year Wilkinson Microwave Anisotropy Probe observations. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data. For other dynamical darkenergy models, we find that some of them, such as the $\\alpha$ darkenergy, constant $w$, generalized Chaplygin gas, and holographic darkenergy models, can provide good fits to the current data, and th...

The DarkEnergy Survey is an imaging survey that covers 5000 square degrees in the Southern hemisphere to map galaxies and gather information on darkenergy. Science requirements for the survey require a 0.5% uncertainty in color, driven by supernova science. The DarkEnergy Survey relies a calibration technique that uses white dwarf stars to set zero points. These white dwarf spectra are fit to models which are used to generate synthetic photometry. These values are compared to the measured values from the survey to verify that the zero points are correct. We present results to date of the spectroscopic reductions of these white dwarf stars in support of the calibrations for the DarkEnergy Survey.

A large number of recent observational data strongly suggest that we live in a flat, accelerating Universe composed of $\\sim$ 1/3 of matter (baryonic + dark) and $\\sim$ 2/3 of an exotic component with large negative pressure, usually named {\\bf DarkEnergy} or {\\bf Quintessence}. The basic set of experiments includes: observations from SNe Ia, CMB anisotropies, large scale structure, X-ray data from galaxy clusters, age estimates of globular clusters and old high redshift galaxies (OHRG's). Such results seem to provide the remaining piece of information connecting the inflationary flatness prediction ($\\Omega_{\\rm{T}} = 1$) with astronomical observations. Theoretically, they have also stimulated the current interest for more general models containing an extra component describing this unknown darkenergy, and simultaneously accounting for the present accelerating stage of the Universe. An overlook in the literature shows that at least five darkenergy candidates have been proposed in the context of general re...

The discovery of cosmic acceleration has stimulated theorists to consider darkenergy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth darkenergy -- modified gravity and interactions of darkenergy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and sp...

In this contribution one examines the coupling of darkenergy to the gauge fields, to neutrinos, and to the Higgs field. In the first case, one shows how a putative evolution of the fundamental couplings of strong and weak interactions via coupling to darkenergy through a generalized Bekenstein-type model may cause deviations on the statistical nuclear decay Rutherford-Soddy law. Existing bounds for the weak interaction exclude any significant deviation. For neutrinos, a perturbative approach is developed which allows for considering viable varying mass neutrino models coupled to any quintessence-type field. The generalized Chaplygin model is considered as an example. For the coupling with the Higgs field one obtains an interesting cosmological solution which includes the unification of darkenergy and dark matter.

Darkenergy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of darkenergy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the darkenergy properties as well as possible.

We extend the dark sector interacting models assuming the darkenergy as the sum of independent contributions $\\rho_{\\Lambda} =\\sum_i\\rho_{\\Lambda i}$, associated with (and interacting with) each of the $i$ material species. We derive the linear scalar perturbations for two interacting darkenergy scenarios, modeling its cosmic evolution and identifying their different imprints in the CMB and matter power spectrum. Our treatment was carried out for two phenomenological motivated expressions of the darkenergy density, $\\rho_\\Lambda(H^2)$ and $\\rho_\\Lambda(R)$. The $\\rho_\\Lambda(H^2)$ description turned out to be a full interacting model, i.e., the darkenergy interacts with everyone material species in the universe, whereas the $\\rho_\\Lambda(R)$ description only leads to interactions between darkenergy and the non-relativistic matter components; which produces different imprints of the two models on the matter power spectrum. A comparison with the Planck 2015 data was made in order to constrain the free para...

The acceleration of the expansion of the universe arises from unknown physical processes involving either new fields in high energy physics or modifications of gravitation theory. It is crucial for our understanding to characterize the properties of the darkenergy or gravity through cosmological observations and compare and distinguish between them. In fact, close consistencies exist between a darkenergy equation of state function w(z) and changes to the framework of the Friedmann cosmological equations as well as direct spacetime geometry quantities involving the acceleration, such as ''geometric darkenergy'' from the Ricci scalar. We investigate these interrelationships, including for the case of super acceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.

In this work we investigate if a small fraction of quarks and gluons, which escaped hadronization and survived as a uniformly spread perfect fluid, can play the role of both dark matter and darkenergy. This fluid, as developed in [1], is characterized by two main parameters: β, related to the amount of quarks and gluons which act as dark matter; and γ, acting as the cosmological constant. We explore the feasibility of this model at cosmological scales using data from type Ia Supernovae (SNeIa), Long Gamma-Ray Bursts (LGRB) and direct observational Hubble data. We find that: (i) in general, β cannot be constrained by SNeIa data nor by LGRB or H(z) data; (ii) γ can be constrained quite well by all three data sets, contributing with ≈78% to the energy–matter content; (iii) when a strong prior on (only) baryonic matter is assumed, the two parameters of the model are constrained successfully.

The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "darkenergy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter (˜5×1015 M ⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an initial "explosion" and darkenergy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly permeating darkenergy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies of the Universe.

Destiny is a simple, direct, low cost mission to determine the properties of darkenergy by obtaining a cosmologically deep supernova (SN) type Ia Hubble diagram. Its science instrument is a 1.65m space telescope, featuring a grism-fed near-infrared (NIR) (0.85-1.7 μm) survey camera/spectrometer with a 0.12 square degree field of view (FOV) covered by a mosaic of 16 2k x 2k HgCdTe arrays. For maximum operational simplicity and instrument stability, Destiny will be deployed into a halo-orbit about the Second Sun-Earth Lagrange Point. During its two-year primary mission, Destiny will detect, observe, and characterize ~3000 SN Ia events over the redshift interval 0.4 Destiny mission data will be used to construct a high-precision Hubble diagram and thereby constrain the darkenergy equation of state. The total range of redshift is sufficient to explore the expansion history of the Universe from an early time, when it was strongly matter-dominated, to the present when darkenergy dominates. The grism-images will provide a spectral resolution of R≡λ/Δλ=75 spectrophotometry that will simultaneously provide broad-band photometry, redshifts, and SN classification, as well as time-resolved diagnostic data, which is valuable for investigating additional SN luminosity diagnostics. Destiny will be used in its third year as a high resolution, wide-field imager to conduct a multicolor NIR weak lensing (WL) survey covering 1000 square degrees. The large-scale mass power spectrum derived from weak lensing distortions of field galaxies as a function of redshift will provide independent and complementary constraints on the darkenergy equation of state. The combination of SN and WL is much more powerful than either technique on its own. Used together, these surveys will have more than an order of magnitude greater sensitivity (by the DarkEnergy Task Force's (DETF) figure of merit) than will be provided by ongoing ground-based projects. The darkenergy parameters, w 0 and w a

Despite the overwhelming evidence for the existence of darkenergy and dark matter, their underlying fundamental physics remains unknown. This review article explores the tantalizing possibility that the dark sector includes new light degrees of freedom that mediate long-range forces on cosmological scales. To ensure consistency with laboratory and solar system tests of gravity, some screening mechanism is necessary to "hide" these degrees of freedom locally. I will focus on two broad classes of screening theories, chameleons and symmetrons, which rely respectively on the scalar field acquiring a large mass or weak coupling in the presence of large ambient matter density.

The equation of state (EoS) of darkenergy $w$ remains elusive despite enormous experimental efforts to pin down its value and its time variation. Yet it is the single most important handle we have in our understanding of one of the most mysterious puzzle in nature, darkenergy. This letter proposes a new method for measuring the EoS of darkenergy by using the gravitational waves (GW) of black hole binaries. The method described here offers an alternative to the standard way of large scale surveys. It is well known that the mass of a black hole changes due to the accretion of darkenergy but at an extremely slow rate. However, a binary of supermassive black holes (SBH) radiates gravitational waves with a power proportional to the masses of these accreting stars and thereby carries information on darkenergy. These waves can propagate through the vastness of structure in the universe unimpeded. The orbital changes of the binary, induced by the energy loss from gravitational radiation, receive a large contribu...

We discuss methods based on Principal Component Analysis for reconstructing the darkenergy equation of state and constraining its evolution, using a combination of Type Ia supernovae at low redshift and spectroscopic measurements of varying fundamental couplings at higher redshifts. We discuss the performance of this method when future better-quality datasets are available, focusing on two forthcoming ESO spectrographs -- ESPRESSO for the VLT and CODEX for the E-ELT -- which include these measurements as a key part of their science cases. These can realize the prospect of a detailed characterization of darkenergy properties all the way up to redshift 4.

The search for constituents that can explain the periods of accelerating expansion of the Universe is a fundamental topic in cosmology. In this context, we investigate how fermionic fields minimally and non-minimally coupled with the gravitational field may be responsible for accelerated regimes during the evolution of the Universe. The forms of the potential and coupling of the model are determined through the technique of the Noether symmetry for two cases. The first case comprises a Universe filled only with the fermion field. Cosmological solutions are straightforwardly obtained for this case and an exponential inflation mediated by the fermion field is possible with a non-minimal coupling. The second case takes account of the contributions of radiation and baryonic matter in the presence of the fermion field. In this case the fermion field plays the role of darkenergy and dark matter, and when a non-minimal coupling is allowed, it mediates a power-law inflation.

Full Text Available In the present paper an attempt is made to develop a fractional integral and differential, deterministic and projective method based on the assumption of the essential discontinuity observed in real systems (note that more than 99% of the volume occupied by an atom in real space has no matter. The differential treatment assumes continuous behaviour (in the form of averaging over the recent past of the system to predict the future time evolution, such that the real history of the system is "forgotten". So it is easy to understand how problems such as unpredictability (chaos arise for many dynamical systems, as well as the great difficulty to connecting Quantum Mechanics (a probabilistic differential theory with General Relativity (a deterministic differential theory. I focus here on showing how the present theory can throw light on crucial astrophysical problems like dark matter and darkenergy.

Full Text Available In the present paper an attempt is made to develop a fractional integral and differential, deterministic and projective method based on the assumption of the essential discontinuity observed in real systems (note that more than 99 % of the volume occupied by an atom in real space has no matter. The differential treatment assumes continuous behaviour (in the form of averaging over the recent past of the system to predict the future time evolution, such that the real history of the system is “forgotten”. So it is easy to understand how problems such as unpredictability (chaos arise for many dynamical systems, as well as the great difficulty to connecting Quantum Mechanics (a probabilistic differential theory with General Relativity (a deterministic differential theory. I focus here on showing how the present theory can throw light on crucial astrophysical problems like dark matter and darkenergy.

The continuing difficulty of achieving a reliable explosion in simulations of core-collapse supernovae, especially for more massive stars, has led to speculation concerning the observable transients that might be produced if such a supernova fails. Even if a prompt outgoing shock fails to form in a collapsing presupernova star, one must still consider the hydrodynamic response of the star to the abrupt loss of mass via neutrinos as the core forms a protoneutron star. Following a suggestion by Nadezhin (1980), we calculate the hydrodynamical responses of typical supernova progenitor stars to the rapid loss of approximately 0.2 to 0.5 M_sun of gravitational mass from their centers. In a red supergiant star, a very weak supernova with total kinetic energy ~ 10^47 erg results. The binding energy of a large fraction of the hydrogen envelope before the explosion is of the same order and, depending upon assumptions regarding the neutrino loss rates, most of it is ejected. Ejection speeds are ~ 100 km/s and luminosit...

We revisit the idea of using varying couplings to probe the nature of darkenergy, in particular by reconstructing its equation of state. We show that this method can be far superior to the standard methods (using type Ia supernovae or weak lensing). We also show that the simultaneous use of measurements of the fine-structure constant $\\alpha$ and the electron-to-proton mass ratio $\\mu$ allows a direct probe of grand unification scenarios. We present forecasts for the sensitivity of this method, both for the near future and for the next generation of spectrographs -- for the latter we focus on the planned CODEX instrument for ESO's Extremely Large Telescope (formerly known as OWL). A high-accuracy reconstruction of the equation of state may be possible all the way up to redshift $z\\sim4$.

We study the implications of Planck data for models of darkenergy (DE) and modified gravity (MG), beyond the cosmological constant scenario. We start with cases where the DE only directly affects the background evolution, considering Taylor expansions of the equation of state, principal component analysis and parameterizations related to the potential of a minimally coupled DE scalar field. When estimating the density of DE at early times, we significantly improve present constraints. We then move to general parameterizations of the DE or MG perturbations that encompass both effective field theories and the phenomenology of gravitational potentials in MG models. Lastly, we test a range of specific models, such as k-essence, f(R) theories and coupled DE. In addition to the latest Planck data, for our main analyses we use baryonic acoustic oscillations, type-Ia supernovae and local measurements of the Hubble constant. We further show the impact of measurements of the cosmological perturbations, such as redshif...

Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant $\\alpha$. Here we take advantage of recent observational progress and use a combination of background cosmological observations of Type Ia supernovas and astrophysical and local measurements of $\\alpha$ to improve constraints on this class of models. We show that the constraints on $\\alpha$ imply that the field dynamics must be extremely slow, leading to a constraint of the present-day darkenergy equation of state $(1+w_0)<2.4\\times10^{-7}$ at the $99.7\\%$ confidence level. Therefore current and forthcoming standard background cosmology observational probes can't distinguish this class of models from a cosmological constant, while detections of $\\alpha$ variations could possibly do so since they would have a characteristic redshift dependence.

Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant α . Here we take advantage of recent observational progress and use a combination of background cosmological observations of type Ia supernovas and astrophysical and local measurements of α to improve constraints on this class of models. We show that the constraints on α imply that the field dynamics must be extremely slow, leading to a constraint of the present-day darkenergy equation of state (1 +w0)<2.4 ×10-7 at the 99.7% confidence level. Therefore current and forthcoming standard background cosmology observational probes cannot distinguish this class of models from a cosmological constant, while detections of α variations could possibly do so since they would have a characteristic redshift dependence.

The fact that the energy densities of darkenergy and matter are similar currently, known as the coincidence problem, is one of the main unsolved problems of cosmology. We present here a phenomenological model in which a spatial curvature of the universe can lead to a transition in the present epoch from a matter dominated universe to a scaling darkenergy dominance in a very natural way. In particular, we show that if the exponential potential of the darkenergy field depends linearly on the spatial curvature density of a closed universe, the observed values of some cosmological parameters can be obtained assuming acceptable values for the present spatial curvature of the universe, and without fine tuning in the only parameter of the model. We also comment on possible variations of this model.

@@ We present a possible explanation to the tiny positive cosmological constant under the frame of AdS5 spacetime embedded by a dS4 brane.We calculate the darkenergy density by summing the zero point energy of massive scalar fields in AdS5 spacetime.Under the assumption that the radius of AdS5 spacetime is of the same magnitude as the radius of observable universe, the darkenergy density in dS4 brane is obtained, which is smaller than the observational value.The reasons are also discussed.

Recently, a model of modified gravity plus single scalar field was proposed, in which the scalar couples both to the standard Riemannian volume form given by the square root of the determinant of the Riemannian metric, as well as to another non-Riemannian volume form given in terms of an auxiliary maximal rank antisymmetric tensor gauge field. This model provides an exact unified description of both darkenergy (via dynamically generated cosmological constant) and dark matter (as a “dust” fluid due to a hidden nonlinear Noether symmetry). In this paper, we test the model against Supernovae type Ia experimental data and investigate the future Universe evolution which follows from it. Our results show that this model has very interesting features allowing various scenarios of Universe evolution and in the same time perfectly fits contemporary observational data. It can describe exponentially expanding or finite expanding Universe and moreover, a Universe with phase transition of first kind. The phase transition occurs to a new, emerging at some time ground state with lower energy density, which affects significantly the Universe evolution.

The Sandage-Loeb (SL) test is a promising method for probing darkenergy because it measures the redshift drift in the spectra of Lyman- α forest of distant quasars, covering the "redshift desert" of 2 ≲ z ≲ 5, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic darkenergy models, i.e., the original holographic darkenergy (HDE) model and the Ricci holographic darkenergy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density Ωm0 and the Hubble constant H 0 in other cosmological observations. For the considered two typical darkenergy models, not only can a 30-year observation of SL test improve the constraint precision of Ωm0 and h dramatically, but can also enhance the constraint precision of the model parameters c and α significantly.

The Big Bang predicted by Friedmann could not be empirically discovered in the 1920th, since global cosmological distances (more than 300-1000 Mpc) were not available for observations at that time. Lemaitre and Hubble studied receding motions of galaxies at local distances of less than 20-30 Mpc and found that the motions followed the (nearly) linear velocity-distance relation, known now as Hubble's law. For decades, the real nature of this phenomenon has remained a mystery, in Sandage's words. After the discovery of darkenergy, it was suggested that the dynamics of local expansion flows is dominated by omnipresent darkenergy, and it is the darkenergy antigravity that is able to introduce the linear velocity-distance relation to the flows. It implies that Hubble's law observed at local distances was in fact the first observational manifestation of darkenergy. If this is the case, the commonly accepted criteria of scientific discovery lead to the conclusion: In 1927, Lemaitre discovered darkenergy and Hubble confirmed this in 1929.

A gravitomagnetic analogue of the London moment in superconductors can explain the anomalous Cooper pair mass excess reported by Janet Tate. Ultimately the gravitomagnetic London moment is attributed to the breaking of the principle of general covariance in superconductors. This naturally implies non-conservation of classical energy-momentum. Possible relation with the manifestation of darkenergy in superconductors is questioned.

Measurements of the luminosity of type Ia supernovae vs. redshift provided the original evidence for the accelerating expansion of the Universe and the existence of darkenergy. Despite substantial improvements in survey methodology, systematic uncertainty in flux calibration dominates the error budget for this technique, exceeding both statistics and other systematic uncertainties. Consequently, any further collection of type Ia supernova data will fail to refine the constraints on the nature of darkenergy unless we also improve the state of the art in astronomical flux calibration to the order of 1%. We describe how these systematic errors arise from calibration of instrumental sensitivity, atmospheric transmission, and Galactic extinction, and discuss ongoing efforts to meet the 1% precision challenge using white dwarf stars as celestial standards, exquisitely calibrated detectors as fundamental metrologic standards, and real-time atmospheric monitoring.

The Sandage-Loeb (SL) test is a promising method for probing darkenergy because it measures the redshift drift in the spectra of Lyman-$\\alpha$ forest of distant quasars, covering the "redshift desert" of $2\\lesssim z\\lesssim5$, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic darkenergy models, i.e., the original holographic darkenergy (HDE) model and the Ricci holographic darkenergy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density $\\Omega_{m0}$ and the Hubble constant $H_0$ in other cosmological observations. For the considered two typical dark e...

The Dark Sector is described by an additional barotropic fluid which evolves adiabatically during the universe's history and whose adiabatic exponent $\\gamma$ is derived from the standard definitions of specific heats. Although in general $\\gamma$ is a function of the redshift, the Hubble parameter and its derivatives, we find that our assumptions lead necessarily to solutions with $\\gamma = $ constant in a FLRW universe. The adiabatic fluid acts effectively as the sum of two distinct components, one evolving like non-relativistic matter and the other depending on the value of the adiabatic index. This makes the model particularly interesting as a way of simultaneously explaining the nature of both DarkEnergy and Dark Matter, at least at the level of the background cosmology. The $\\Lambda$CDM model is included in this family of theories when $\\gamma = 0$. We fit our model to SNIa, $H(z)$ and BAO data, discussing the model selection criteria. The implications for the early-universe and the growth of small per...

The standard \\LambdaCDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform darkenergy background, represented by Einstein's cosmological constant, and experience its repulsive antigravity action. Can darkenergy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we focus now on the Virgo Cluster and the flow of expansion around it. We interpret the Hubble diagram, from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Our conclusions are: 1. The interplay between the gravity of the cluster and the antigravity of the darkenergy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the qu...

The coalescence of a binary neutron star (BNS) pair is expected to produce gravitational waves (GW) and electromagnetic (EM) radiation, both of which may be detectable with currently available instruments. We describe a search for a theoretically predicted r-process optical transient from these mergers, dubbed the kilonova (KN), using griz broadband data from the DarkEnergy Survey Supernova Program (DES-SN). Some models predict KNe to be redder, shorter-lived, and dimmer than supernovae (SNe), but at present the event rate of KNe is poorly constrained. We simulate observations of KN and SN light curves with the Monte-Carlo simulation code SNANA to optimize selection requirements, determine search efficiency, and predict SN backgrounds. We also perform an analysis using fake point sources on images to account for anomalous efficiency losses from difference-imaging on bright low-redshift galaxies. Our analysis of the first two seasons of DES-SN data results in 0 events, and is consistent with our prediction of...

We present a cosmological analysis of the Lick Observatory Supernova Search (LOSS) Type Ia supernova (SN Ia) photometry sample introduced by Ganeshalingam et al. (2010). These SNe provide an effective anchor point to estimate cosmological parameters when combined with datasets at higher redshift. The data presented by Ganeshalingam et al. (2010) have been rereduced in the natural system of the KAIT and Nickel telescopes to minimise systematic uncertainties. We have run the light-curve-fitting software SALT2 on our natural-system light curves to measure light-curve parameters for LOSS light curves and available SN Ia datasets in the literature. We present a Hubble diagram of 586 SNe in the redshift range z=0.01-1.4 with a residual scatter of 0.176 mag. Of the 226 low-z objects in our sample, 91 objects are from LOSS, including 45 SNe without previously published distances. Assuming a flat Universe, we find that the best fit for the darkenergy equation-of-state parameter w = -0.86^+0.13_-0.16 (stat) +- 0.11 (s...

We describe an algorithm for identifying point-source transients and moving objects on reference-subtracted optical images containing artifacts of processing and instrumentation. The algorithm makes use of the supervised machine learning technique known as Random Forest. We present results from its use in the DarkEnergy Survey Supernova program (DES-SN), where it was trained using a sample of 898,963 signal and background events generated by the transient detection pipeline. After reprocessing the data collected during the first DES-SN observing season (2013 September through 2014 February) using the algorithm, the number of transient candidates eligible for human scanning decreased by a factor of 13.4, while only 1.0% of the artificial Type Ia supernovae (SNe) injected into search images to monitor survey efficiency were lost, most of which were very faint events. Here we characterize the algorithm’s performance in detail, and we discuss how it can inform pipeline design decisions for future time-domain imaging surveys, such as the Large Synoptic Survey Telescope and the Zwicky Transient Facility. An implementation of the algorithm and the training data used in this paper are available at at http://portal.nersc.gov/project/dessn/autoscan.

We describe an algorithm for identifying point-source transients and moving objects on reference-subtracted optical images containing artifacts of processing and instrumentation. The algorithm makes use of the supervised machine learning technique known as Random Forest. We present results from its use in the DarkEnergy Survey Supernova program (DES-SN), where it was trained using a sample of 898,963 signal and background events generated by the transient detection pipeline. After reprocessing the data collected during the first DES-SN observing season (2013 September through 2014 February) using the algorithm, the number of transient candidates eligible for human scanning decreased by a factor of 13.4, while only 1.0 percent of the artificial Type Ia supernovae (SNe) injected into search images to monitor survey efficiency were lost, most of which were very faint events. Here we characterize the algorithm's performance in detail, and we discuss how it can inform pipeline design decisions for future time-domain imaging surveys, such as the Large Synoptic Survey Telescope and the Zwicky Transient Facility.

We describe an algorithm for identifying point-source transients and moving objects on reference-subtracted optical images containing artifacts of processing and instrumentation. The algorithm makes use of the supervised machine learning technique known as Random Forest. We present results from its use in the DarkEnergy Survey Supernova program (DES-SN), where it was trained using a sample of 898,963 signal and background events generated by the transient detection pipeline. After reprocessing the data collected during the first DES-SN observing season (Sep. 2013 through Feb. 2014) using the algorithm, the number of transient candidates eligible for human scanning decreased by a factor of 13.4, while only 1 percent of the artificial Type Ia supernovae (SNe) injected into search images to monitor survey efficiency were lost, most of which were very faint events. Here we characterize the algorithm's performance in detail, and we discuss how it can inform pipeline design decisions for future time-domain imaging...

If darkenergy interacts with dark matter, there is a change in the background evolution of the universe, since the dark matter density no longer evolves as a^{-3}. In addition, the non-gravitational interaction affects the growth of structure. In principle, these changes allow us to detect and constrain an interaction in the dark sector. Here we investigate the growth factor and the weak lensing signal for a class of interacting darkenergy models. In these models, the interaction is determined by a linear combination of the dark sector densities, with constant energy transfer rates. Assuming a normalization to today's values of dark matter density and overdensity, the signal of the interaction is an enhancement (suppression) of both the growth factor and the lensing power, when the energy transfer in the background is from dark matter to darkenergy (darkenergy to dark matter).

We present ultra low energy results taken with the novel Spherical Proportional Counter. The energy threshold has been pushed down to about 25 eV and single electrons are clearly collected and detected. To reach such performance low energy calibration systems have been successfully developed: - A pulsed UV lamp extracting photoelectrons from the inner surface of the detector - Various radioactive sources allowing low energy peaks through fluorescence processes. The bench mark result is the observation of a well resolved peak at 270 eV due to carbon fluorescence which is unique performance for such large-massive detector. It opens a new window in dark matter and low energy neutrino search and may allow detection of neutrinos from a nuclear reactor or from supernova via neutrino-nucleus elastic scattering

We present a simple (microscopic) model in which bulk viscosity plays a role in explaining the present acceleration of the universe. The effect of bulk viscosity on the Friedmann equations is to turn the pressure into an "effective" pressure containing the bulk viscosity. For a sufficiently large bulk viscosity, the effective pressure becomes negative and could mimic a darkenergy equation of state. Our microscopic model includes self-interacting spin-zero particles (for which the bulk viscosity is known) that are added to the usual energy content of the universe. We study both background equations and linear perturbations in this model. We show that a darkenergy behavior is obtained for reasonable values of the two parameters of the model (i.e. the mass and coupling of the spin-zero particles) and that linear perturbations are well-behaved. There is no apparent fine tuning involved. We also discuss the conditions under which hydrodynamics holds, in particular that the spin-zero particles must be in local eq...

We find that deviation from the virial equilibrium of the Abell Cluster A586 yields evidence of the interaction between dark matter and darkenergy. We argue that this interaction might imply a violation of the Equivalence Principle. Our analysis show that evidence is found in the context of two different models of darkenergy-dark matter interaction.

I review the current status of Big Bang Cosmology, with emphasis on current issues in dark matter, darkenergy, and galaxy formation. These topics motivate many of the current goals of experimental cosmology which range from targeting the nature of darkenergy and dark matter to probing the epoch of the first stars and galaxies.

Using current observations forecast type Ia supernovae (SNe Ia) Joint Lightcurve Analysis (JLA) binned and baryon acoustic oscillations (BAO), in this paper we investigate six bidimensional darkenergy parameterizations in order to explore which has more constraining power. Our results indicate that for Taylor series-like parameterizations at second order in redshift $z$, the tension ($\\sigma$-distance) between these data sets seems to be reduced and their behaviour are $

We propose a heuristic unification of dark matter and darkenergy in terms of a single dark fluid with a logotropic equation of state $P=A\\ln(\\rho/\\rho_P)$, where $\\rho$ is the rest-mass density, $\\rho_P$ is the Planck density, and $A$ is the logotropic temperature. The energy density $\\epsilon$ is the sum of a rest-mass energy term $\\rho c^2$ mimicking dark matter and an internal energy term $u(\\rho)=-P(\\rho)-A$ mimicking darkenergy. The logotropic temperature is approximately given by $A \\simeq \\rho_{\\Lambda}c^2/\\ln(\\rho_P/\\rho_{\\Lambda})\\simeq\\rho_{\\Lambda}c^2/[123 \\ln(10)]$, where $\\rho_{\\Lambda}$ is the cosmological density. More precisely, we obtain $A=2.13\\times 10^{-9} \\, {\\rm g}\\, {\\rm m}^{-1}\\, {\\rm s}^{-2}$ that we interpret as a fundamental constant. At the cosmological scale, this model fullfills the same observational constraints as the $\\Lambda$CDM model. However, it has a nonzero velocity of sound and a nonzero Jeans length which, at the beginning of the matter era, is about $\\lambda_J=40.4\\,...

For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 darkenergy over models without darkenergy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the "Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra. Our CMB-only measurement of the darkenergy density Omega(delta) confirms other measurements from supernovae, galaxy clusters and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.

The cosmological constant and many other possible origins for acceleration of the cosmic expansion possess variations in the darkenergy properties slow on the Hubble time scale. Given that models with more rapid variation, or even phase transitions, are possible though, we examine the fineness in redshift with which cosmological probes can realistically be employed, and what constraints this could impose on darkenergy behavior. In particular, we discuss various aspects of baryon acoustic oscillations, and their use to measure the Hubble parameter H(z). We find that currently considered cosmological probes have an innate resolution no finer than Δz≈0.2 0.3.

Atomic interferometry can be used to probe darkenergy models coupled to matter. We consider the constraints coming from recent experimental results on models generalising the inverse power law chameleons such as $f(R)$ gravity in the large curvature regime, the environmentally dependent dilaton and symmetrons. Using the tomographic description of these models, we find that only symmetrons with masses smaller than the darkenergy scale can be efficiently tested. In this regime, the resulting constraints complement the bounds from the E\\"otwash experiment and exclude small values of the symmetron self-coupling.

We investigate a possible connection between the suppression of the power at low multipoles in the CMB spectrum and the late time acceleration. We show that, assuming a cosmic IR/UV duality between the UV cutoff and a global infrared cutoff given by the size of the future event horizon, the equation of state of the darkenergy can be related to the apparent cutoff in the CMB spectrum. The present limits on the equation of state of darkenergy are shown to imply an IR cutoff in the CMB multipole interval of 9>l>8.5.

Full Text Available Recently, nonminimal coupling between a noncanonical scalar field and gravity in the framework of teleparallelism has been proposed. Noncanonical scalar field is tachyon field, and the model is known as tachyonic teleparallel darkenergy. Here, we perform a dynamical analysis of the model, find its critical points, and study their stability. We find that all the critical points are darkenergy dominated solutions corresponding to an accelerating universe. It is also shown that there exist two critical lines which are stable attractors of the model.

A unification of dark matter and darkenergy in terms of a logotropic perfect dark fluid has recently been proposed, where deviations with respect to the standard $\\Lambda {\\rm CDM}$ model are dependent on a single parameter $B$. In this paper we show that the requirement that the linear growth of cosmic structures on comoving scales larger than $8 h^{-1} \\, {\\rm Mpc}$ is not significantly affected with respect to the standard $\\Lambda {\\rm CDM}$ result provides the strongest constraint to date on the model ($B <6 \\times 10^{-7}$), an improvement of more than three orders of magnitude over previous constraints on the value of $B$. We further show that this constraint rules out the logotropic Unified DarkEnergy model as a possible solution to the small scale problems of the $\\Lambda$CDM model, including the cusp problem of Dark Matter halos or the missing satellite problem, as well as the original version of the model where the Planck energy density was taken as one of the two parameters characterizing the...

The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of darkenergy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of darkenergy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local darkenergy constitute the main characteristic feature of these systems.

Full Text Available We present a conjugate analysis of two different darkenergy models, namely the Barboza–Alcaniz parameterization and the phenomenologically-motivated Hobbit model, investigating both their agreement with observational data and their thermodynamical properties. We successfully fit a wide dataset including the Hubble diagram of Type Ia Supernovae, the Hubble rate expansion parameter as measured from cosmic chronometers, the baryon acoustic oscillations (BAO standard ruler data and the Planck distance priors. This analysis allows us to constrain the model parameters, thus pointing at the region of the wide parameters space, which is worth focusing on. As a novel step, we exploit the strong connection between gravity and thermodynamics to further check models’ viability by investigating their thermodynamical quantities. In particular, we study whether the cosmological scenario fulfills the generalized second law of thermodynamics, and moreover, we contrast the two models, asking whether the evolution of the total entropy is in agreement with the expectation for a closed system. As a general result, we discuss whether thermodynamic constraints can be a valid complementary way to both constrain darkenergy models and differentiate among rival scenarios.

Based on dramatic observations of the CMB with WMAP and of Type Ia supernovae with the Hubble Space Telescope and ground-based facilities, it is now generally believed that the Universe's expansion is accelerating. Within the context of standard cosmology, the Universe must therefore contain a third `dark' component of energy, beyond matter and radiation. However, the current data are still deemed insufficient to distinguish between an evolving darkenergy component and the simplest model of a time-independent cosmological constant. In this paper, we examine the role played by our cosmic horizon R0 in our interrogation of the data, and reach the rather firm conclusion that the existence of a cosmological constant is untenable. The observations are telling us that R0=c t0, where t0 is the perceived current age of the Universe, yet a cosmological constant would drive R0 towards ct (where t is the cosmic time) only once, and that would have to occur right now. In contrast, scaling solutions simultaneously elimin...

We consider using future redshift surveys with the Large Sky Area MultiObject Fiber Spectroscopic Telescope (LAMOST) to constrain the equation of state of darkenergy ω. We analyze the Alcock & Paczynski (AP) effect imprinted on the two-point correlation function of galaxies in redshift space. The Fisher matrix analysis is applied to estimate the expected error bounds of ω0 and ωa from galaxy redshift surveys, ω0 and ωa being the two parameters in the equation of state parametrization ω(z) = ω0 + ωaz/(1 -+ z). Strong degeneracies between ω0 and ωa are found. The direction of the degeneracy in ω0 - ωa plane, however, rotates counter-clockwise as the redshift increases. LAMOST can potentially contribute in the redshift range up to 0.5. In combination with other high redshift surveys, such as the proposed KiloAperture Optical Spectrograph project (KAOS), the joint constraint derived from galaxy surveys at different redshift ranges is likely to efficiently break the degeneracy of ω0 and ωa. We do not anticipate that the nature of darkenergy can be well constrained with LAMOST alone, but it may help to reduce the error bounds expected from other observations, such as the Supernova/Acceleration Probe (SNAP).

The DarkEnergy Space Telescope (DESTINY) is an all-grism NIR 1.8 m survey camera optimized to return richly sampled Hubble diagrams of Type Ia and Type II supernovae (SN) over the redshift range 0.5 the universe as a function of time, and characterizing the nature of the so-called "darkenergy" component of the universe. SN will be discovered by repeated imaging of a 7.5 square-degree area located at the north ecliptic poles. Grism spectra with resolving power λ/Δ λ = R ˜ 75 will provide broad-band spectrophotometry, redshifts, SN classification, as well as valuable time-resolved diagnostic data for understanding the SN explosion physics. This methodology features only a single mode of operation with no time-critical interactions, a single detector technology, and a single instrument. Although grism spectroscopy is slow compared to SN detection in any single broad-band filter for photometry, or to conventional slit spectra for spectral diagnostics, the multiplex advantage of being able to observe a large field-of-view simultaneously over a full octave in wavelength makes this approach highly competitive.

We describe a mission concept for a 1.8-meter near-infrared (NIR) grism-mode space telescope optimized to return richly sampled Hubble diagrams of Type Ia and Type II supernovae (SNe) over the redshift range 0.5 the Universe as a function of time, and characterizing the nature of darkenergy. The central concept for our proposed DarkEnergy Space Telescope (DESTINY) is an all-grism NIR survey camera. SNe will be discovered by repeated imaging of an area located at the north ecliptic pole. Grism spectra with resolving power l/Dl = R * 100 will provide broad-band spectrophotometry, redshifts, SNe classification, as well as valuable time-resolved diagnostic data for understanding the SN explosion physics. Our approach features only a single mode of operation, a single detector technology, and a single instrument. Although grism spectroscopy is slow compared to SN detection in any single broad-band filter for photometry, or to conventional slit spectra for spectral diagnostics, the multiplex advantage of observing a large field-of-view over a full octave in wavelength simultaneously makes this approach highly competitive. In this poster we present exposure simulations to demonstrate the efficiency of the DESTINY approach.

The Destiny space telescope is a candidate architecture for the NASA-DOE Joint DarkEnergy Mission (JDEM). This paper describes some of the scientific and observational issues that will be explored as part of our mission concept study. The Destiny ~1.8-meter near-infrared (NIR) grism-mode space telescope would gather a census of type Ia and type II supernovae (SN) over the redshift range 0.5 the Universe as a function of time and characterizing the nature of darkenergy. The central concept is a wide-field, all-grism NIR survey camera. Grism spectra with 2-pixel resolving power R~70-100 will provide broad-band spectrophotometry, redshifts, SN classification, as well as valuable time-resolved diagnostic data for understanding the SN explosion physics. Spectra from all objects within the 1° x 0.25° FOV will be obtained on a large HgCdTe focal plane array. Our methodology requires only a single mode of operation, a single detector technology, and a single instrument.

According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use a scale parameter calculated from the volume-averaged increments of local scale parameters at each time step in an otherwise standard cosmological N-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical estimation of the effect of non-linear evolution of structure on the expansion rate. Using our algorithm, a simulation with an initial Ωm = 1 Einstein-de Sitter setting closely tracks the expansion and structure growth history of the Λ cold dark matter (ΛCDM) cosmology. Due to small but characteristic differences, our model can be distinguished from the ΛCDM model by future precision observations. Moreover, our model can resolve the emerging tension between local Hubble constant measurements and the Planck best-fitting cosmology. Further improvements to the simulation are necessary to investigate light propagation and confirm full consistency with cosmic microwave background observations.

We extend the Loop Quantum Cosmology matter bounce scenario in order to include a darkenergy era, which ends abruptly at a Rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario", the Universe is contracting from an initial non-causal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, thus the model is described by a darkenergy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the darkenergy era is quintessential like which follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the darkenergy era, a Rip singularity exists, where the scale factor and Hubble rate diverge, however the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, firstly th...

@@ Selection statics of the Akaike information criterion (AIC) model and the Bayesian information criterion (BIC)model are applied to the Λ-cold dark matter (ΛCDM) cosmological model, the constant equation of state of darkenergy, w =constant, and the parametrized equation of state of darkenergy, w(z) = w0 + w1z/(1 + z),to determine which one is the better cosmological model to describe the evolution of the universe by combining the recent cosmic observational data including Sne Ia, the size of baryonic acoustic oscillation (BAO) peak from SDSS, the three-year WMAP CMB shift parameter. The results show that AIC, BIC and current datasets are not powerful enough to discriminate one model from the others, though odds suggest differences between them.

A strong instrumentation and detector R&D program has enabled the current generation of cosmic frontier surveys. A small investment in R&D will continue to pay dividends and enable new probes to investigate the accelerated expansion of the universe. Instrumentation and detector R&D provide critical training opportunities for future generations of experimentalists, skills that are important across the entire Department of Energy High Energy Physics program.

A strong instrumentation and detector R&D program has enabled the current generation of cosmic frontier surveys. A small investment in R&D will continue to pay dividends and enable new probes to investigate the accelerated expansion of the universe. Instrumentation and detector R&D provide critical training opportunities for future generations of experimentalists, skills that are important across the entire Department of Energy High Energy Physics program.

We report on precision resonance spectroscopy measurements of quantum states of ultracold neutrons confined above the surface of a horizontal mirror by the gravity potential of the Earth. Resonant transitions between several of the lowest quantum states are observed for the first time. These measurements demonstrate, that Newton's inverse square law of Gravity is understood at micron distances on an energy scale of~$10^{-14}$~eV. At this level of precision we are able to provide constraints on any possible gravity-like interaction. In particular, a darkenergy chameleon field is excluded for values of the coupling constant~$\\beta > 5.8\\times10^8$ at~95% confidence level~(C.L.), and an attractive (repulsive) dark matter axion-like spin-mass coupling is excluded for the coupling strength $g_sg_p > 3.7\\times10^{-16}$~($5.3\\times10^{-16}$)~at a Yukawa length of~$\\lambda = 20$~{\\textmu}m~(95% (C.L.).

Solutions to the energy-independent (gray) radiative transfer equations are compared to results of Monte Carlo simulations of the \\Ni\\ and \\Co\\ radioactive decay \\GR\\ energy deposition in supernovae. The comparison shows that an effective, purely absorptive, gray opacity, \\KG\\ \\sim (0.06 \\pm 0.01)Y_e cm^2 g^{-1}, where Y_e is the total number of electrons per baryon, accurately describes the interaction of \\GRs\\ with the cool supernova gas and the local \\GR\\ energy deposition within the gas. The nature of the \\GR\\ interaction process (dominated by Compton scattering in the relativistic regime) creates a weak dependence of \\KG\\ on the optical thickness of the (spherically symmetric) supernova atmosphere: The maximum value of \\KG\\ applies during optically thick conditions when individual \\GRs\\ undergo multiple scattering encounters and the lower bound is reached at the phase characterized by a total Thomson optical depth to the center of the atmosphere \\te\\ \\LA\\ 1. Our results quantitatively confirm that the qu...

In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, darkenergy with an equation-of-state parameter $w < -1$ (known as phantom darkenergy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the value of best fit from Planck and WMAP9 for present-day $w$ is indeed less than $-1$. We find that it is not as obvious as one might think that phantom darkenergy has negative kinetic energy categorically. Staying within the confines of observational constraints and general relativity, for which there is good experimental validation, we consider a few reasonable departures from the standard 0th-order framework in an attempt to see if negative kinetic energy can be avoided in these settings despite an apparent $wenergy tensor, and we ...

In this paper bulk viscosity is introduced to describe the effects of cosmic non-perfect fluid on the cosmos evolution and to build the unified darkenergy （DE） with （dark） matter models. Also we derive a general relation between the bulk viscosity form and Hubble parameter that can provide a procedure for the viscosity DE model building. Especially, a redshift dependent viscosity parameter ζ ∝ λ0 ＋λ1（1 ＋z）n proposed in the previous work [X.H. Meng and X. Dou, Commun. Theor. Phys. B2 （2009） 377] is investigated extensively in this present work. Further more we use the recently released supernova dataset （the Constitution dataset） to constrain the model parameters. In order to differentiate the proposed concrete darkenergy models from the well known ACDM model, statefinder diagnostic method is applied to this bulk viscosity model, as a complementary to the Om parameter diagnostic and the deceleration parameter analysis performed by us before. The DE model evolution behavior and tendency are shown in the plane of the statefinder diagnostic parameter pair {τ, s} as axes where the fixed point represents the A CDM model The possible singularity property in this bulk viscosity cosmology is also discussed to which we can conclude that in the different parameter regions chosen properly, this concrete viscosity DE model can have various late evolution behaviors and the late time singularity could be avoided. We also calculate the cosmic entropy in the bulk viscosity darkenergy frame, and find that the total entropy in the viscosity DE model increases monotonously with respect to the scale factor evolution, thus this monotonous increasing property can indicate an arrow of time in the universe evolution, though the quantum version of the arrow of time is still very puzzling.

最近的宇宙学观测表明,人类熟悉的原子物质(重子物质)只占宇宙总能量的4％左右,而剩下的能量成分都是看不见的暗物质和暗能量,其中暗物质占23％,暗能量占73％.当前,暗物质和暗能量的起源和物理本质都不清楚,揭开它们的神秘本质是现代基础科学所面临的最大挑战之一.暗物质虽然神秘,但是它所产生的引力是和原子物质一样的正常引力.而暗能量就不同了,它更加神秘莫测,它产生的引力实际上是一种排斥力.正是由于暗能量的排斥力的驱动,我们的宇宙现在正在加速膨胀.暗能量在当前的物理学理论框架下面临着严重的问题.实际上,它的物理本性和量子引力理论有着深刻的联系.因此,暗能量的理论研究将为自下而上地建立一个完整的量子引力理论提供重要的线索.在简要论述了与暗能量相关的各种问题来龙去脉的基础上,描述了这个领域的概况.%Recent cosmological observations show that, atoms (or, baryons) only occupy 4% of the cosmic contents, and other 96% components are nonluminous dark matter and darkenergy, explaining 23% and 73% of the total energy of the universe, respectively. Currently, the natures of dark matter and darkenergy are both enigmatic, and so the revelation of their exotic natures raises one of the biggest challenges for the modern fundamental science. Darkenergy is more mysterious than dark matter in that its gravity is repulsive, driving the current expansion of the universe to accelerate. Darkenergy suffers from severe theoretical problems within the current framework of physics. In fact, the physical nature of darkenergy is in deep connection with the underlying quantum gravity theory. Thus, the theoretical studies on darkenergy may provide significant clues for the bottom-up exploration of a full quantum theory of gravitation. This paper will explain various darkenergy-relevant problems, and briefly

The DarkEnergy Spectroscopic Instrument (DESI) is a Stage IV ground-based darkenergy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar spectroscopic redshift survey. The DESI instrument consists of a new wide-field (3.2 deg. linear field of view) corrector plus a multi-object spectrometer with up to 5000 robotically positioned optical fibers and will be installed at prime focus on the Mayall 4m telescope at Kitt Peak, Arizona. The fibers feed 10 three-arm spectrographs producing spectra that cover a wavelength range from 360-980 nm and have resolution of 2000-5500 depending on the wavelength. The DESI instrument is designed for a 14,000 sq. deg. multi-year survey of targets that trace the evolution of darkenergy out to redshift 3.5 using the redshifts of luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars. DESI is the successor to the successful Stage-III BOSS spectroscopic redshift survey and complements imaging surveys such as the Stage-III DarkEnergy Survey (DES, currently operating) and the Stage-IV Large Synoptic Survey Telescope (LSST, planned start early in the next decade).

It is argued that the discovery of cosmic acceleration could have been anticipated on thermodynamic grounds, namely, the generalized second law and the approach to equilibrium at large scale factor. Therefore, the existence of darkenergy -or equivalently, some modified gravity theory- should have been expected. In general, cosmological models that satisfy the above criteria show compatibility with observational data.

It is shown that Beck's electromagnetic model of darkenergy in superconductors can account for the gravitomagnetic London moment, which has been conjectured by the author to explain the Cooper pair's mass excess reported by Cabrera and Tate. A new Einstein-Planck regime for gravitation in condensed matter is proposed as a natural scale to host the gravitoelectrodynamic properties of superconductors.

In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the darkenergy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require an urgent solution for the sake of the internal consistency of theoretical physics.

In this work we review briefly the origin and history of the cosmological constant and its recent reincarnation in the form of the darkenergy component of the universe. We also comment on the fundamental problems associated to its existence and magnitude which require and urgent solution for the sake of the internal consistency of theoretical physics.

By using a linearized non-vacuum late time solution in Brans-Dicke cosmology, we account for the 75% darkenergy contribution but not for approximately 23% dark matter contribution to the present day energy density of the universe.

We propose a heuristic unification of dark matter and darkenergy in terms of a single ;dark fluid; with a logotropic equation of state P = Aln ⁡ (ρ /ρP), where ρ is the rest-mass density, ρP = 5.16 ×1099gm-3 is the Planck density, and A is the logotropic temperature. The energy density ɛ is the sum of a rest-mass energy term ρc2 ∝a-3 mimicking dark matter and an internal energy term u (ρ) = - P (ρ) - A = 3 Aln ⁡ a + C mimicking darkenergy (a is the scale factor). The logotropic temperature is approximately given by A ≃ρΛc2 / ln ⁡ (ρP /ρΛ) ≃ρΛc2 / [ 123 ln ⁡ (10) ], where ρΛ = 6.72 ×10-24gm-3 is the cosmological density and 123 is the famous number appearing in the ratio ρP /ρΛ ∼10123 between the Planck density and the cosmological density. More precisely, we obtain A = 2.13 ×10-9gm-1s-2 that we interpret as a fundamental constant. At the cosmological scale, our model fulfills the same observational constraints as the ΛCDM model (they will differ in about 25 Gyrs when the logotropic universe becomes phantom). However, the logotropic dark fluid has a nonzero speed of sound and a nonzero Jeans length which, at the beginning of the matter era, is about λJ = 40.4pc, in agreement with the minimum size of the dark matter halos observed in the universe. The existence of a nonzero Jeans length may solve the missing satellite problem. At the galactic scale, the logotropic pressure balances the gravitational attraction, providing halo cores instead of cusps. This may solve the cusp problem. The logotropic equation of state generates a universal rotation curve that agrees with the empirical Burkert profile of dark matter halos up to the halo radius. In addition, it implies that all the dark matter halos have the same surface density Σ0 =ρ0rh = 141M⊙ /pc2 and that the mass of dwarf galaxies enclosed within a sphere of fixed radius ru = 300pc has the same value M300 = 1.93 ×107M⊙, in remarkable agreement with the observations

Full Text Available We propose a heuristic unification of dark matter and darkenergy in terms of a single “dark fluid” with a logotropic equation of state P=Aln⁡(ρ/ρP, where ρ is the rest-mass density, ρP=5.16×1099gm−3 is the Planck density, and A is the logotropic temperature. The energy density ϵ is the sum of a rest-mass energy term ρc2∝a−3 mimicking dark matter and an internal energy term u(ρ=−P(ρ−A=3Aln⁡a+C mimicking darkenergy (a is the scale factor. The logotropic temperature is approximately given by A≃ρΛc2/ln⁡(ρP/ρΛ≃ρΛc2/[123ln⁡(10], where ρΛ=6.72×10−24gm−3 is the cosmological density and 123 is the famous number appearing in the ratio ρP/ρΛ∼10123 between the Planck density and the cosmological density. More precisely, we obtain A=2.13×10−9gm−1s−2 that we interpret as a fundamental constant. At the cosmological scale, our model fulfills the same observational constraints as the ΛCDM model (they will differ in about 25 Gyrs when the logotropic universe becomes phantom. However, the logotropic dark fluid has a nonzero speed of sound and a nonzero Jeans length which, at the beginning of the matter era, is about λJ=40.4pc, in agreement with the minimum size of the dark matter halos observed in the universe. The existence of a nonzero Jeans length may solve the missing satellite problem. At the galactic scale, the logotropic pressure balances the gravitational attraction, providing halo cores instead of cusps. This may solve the cusp problem. The logotropic equation of state generates a universal rotation curve that agrees with the empirical Burkert profile of dark matter halos up to the halo radius. In addition, it implies that all the dark matter halos have the same surface density Σ0=ρ0rh=141M⊙/pc2 and that the mass of dwarf galaxies enclosed within a sphere of fixed radius ru=300pc has the same value M300=1.93×107M⊙, in remarkable agreement with the observations [Donato et al. [10

We investigate the breaking of global statistical isotropy caused by a darkenergy component with an energy-momentum tensor which has point symmetry, that could represent a cubic or hexagonal crystalline lattice. In such models Gaussian, adiabatic initial conditions created during inflation can lead to anisotropies in the cosmic microwave background whose spherical harmonic coefficients are correlated, contrary to the standard assumption. We develop an adaptation of the line of sight integration method that can be applied to models where the background energy-momentum tensor is isotropic, but whose linearized perturbations are anisotropic. We then show how this can be applied to the cases of cubic and hexagonal symmetry. We compute quantities which show that such models are indistinguishable from isotropic models even in the most extreme parameter choices, in stark contrast to models with anisotropic initial conditions based on inflation. The reason for this is that the darkenergy based models contribute to ...

The observed acceleration expansion of the universe was thought attribute to a mysterious darkenergy in the framework of the classical general relativity. The darkenergy behaves very similar with a vacuum energy in quantum mechanics. However, once the quantum effects are seriously taken into account, it predicts a wrong order of the vacuum energy and leads to a severe fine-tuning, known as the cosmological constant problem. We abandon the standard interpretation that time is a global parameter in quantum mechanics, replace it by a quantum dynamical variable playing the role of an operational quantum clock system. In the framework of reinterpretation of time, we find that the synchronization of two quantum clocks distance apart can not be realized in all rigor at quantum level. Thus leading to an intrinsic quantum uncertainty of simultaneity between spatial interval, which implies a visional vacuum energy fluctuation and gives an observed darkenergy density $\\rho_{de}=\\frac{6}{\\pi}L_{P}^{-2}L_{H}^{-2}$, whe...

We investigate a spatially flat Friedmann-Robertson-Walker (FRW) scenario with two interacting components, dark matter and variable vacuum energy (VVE) densities, plus two decoupled components, one is a baryon term while the other behaves as a radiation component. We consider a linear interaction in the derivative dark component density. We apply the $\\chi^2$ method to the observational Hubble data for constraining the cosmological parameters and analyze the amount of darkenergy in the radiation era for the model. It turns out that our model fulfills the severe bound of $\\Omega_{x}(z\\simeq 1100)<0.009$ at $2\\sigma$ level, so is consistent with the recent analysis that includes cosmic microwave background anisotropy measurements from Planck survey, the future constraints achievable by Euclid and CMBPol experiments, reported for the behavior of the darkenergy at early times, and fulfills the stringent bound $\\Omega_{x}(z\\simeq 10^{10})<0.04$ at $2\\sigma$ level in the big-bang nucleosynthesis epoch. We a...

The discovery of cosmic acceleration has stimulated theorists to consider darkenergy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth darkenergy -- modified gravity and interactions of darkenergy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and spectroscopy and radio observations. In the coming decade, searches for these effects have the potential for discovering fundamental new physics. We discuss how the searches can be carried out using experiments that are already under way or with modest adaptations of existing telescopes or planned experiments. The accompanying paper on the Growth of Cosmic Structure describes complementary tests of gravity with observations of large-scale structure.

We compare some popular darkenergy models under the assumption of a flat universe by using the latest observational data including the type Ia supernovae Constitution compilation,the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey,the cosmic microwave background measurement given by the seven-year Wilkinson Microwave Anisotropy Probe observations and the determination of H0 from the Hubble Space Telescope.Model comparison statistics such as the Bayesian and Akaike information criteria are applied to assess the worth of the models.These statistics favor models that give a good fit with fewer parameters.Based on this analysis,we find that the simplest cosmological constant model that has only one free parameter is still preferred by the current data.For other dynamical darkenergy models,we find that some of them,such as the αdarkenergy,constant w,generalized Chaplygin gas,Chevalliear-Polarski-Linder parametrization,and holographic darkenergy models,can provide good fits to the current data,and three of them,namely,the Ricci darkenergy,agegraphic darkenergy,and Dvali-Gabadadze-Porrati models,are clearly disfavored by the data.

Recent astronomical observations have indicated that the Universe is in a phase of accelerated expansion. While there are many cosmological models which try to explain this phenomenon, we focus on the interacting CDM model where an interaction between the darkenergy and dark matter sectors takes place. This model is compared to its simpler alternative—the CDM model. To choose between these models the likelihood ratio test was applied as well as the model comparison methods (employing Occam's principle): the Akaike information criterion (AIC), the Bayesian information criterion (BIC) and the Bayesian evidence. Using the current astronomical data: type Ia supernova (Union2.1), , baryon acoustic oscillation, the Alcock-Paczynski test, and the cosmic microwave background data, we evaluated both models. The analyses based on the AIC indicated that there is less support for the interacting CDM model when compared to the CDM model, while those based on the BIC indicated that there is strong evidence against it in favor of the CDM model. Given the weak or almost non-existing support for the interacting CDM model and bearing in mind Occam's razor we are inclined to reject this model.

Recent astronomical observations have indicated that the Universe is in a phase of accelerated expansion. While there are many cosmological models which try to explain this phenomenon, we focus on the interacting ΛCDM model where an interaction between the darkenergy and dark matter sectors takes place. This model is compared to its simpler alternative—the ΛCDM model. To choose between these models the likelihood ratio test was applied as well as the model comparison methods (employing Occam’s principle): the Akaike information criterion (AIC), the Bayesian information criterion (BIC) and the Bayesian evidence. Using the current astronomical data: type Ia supernova (Union2.1), h(z), baryon acoustic oscillation, the Alcock–Paczynski test, and the cosmic microwave background data, we evaluated both models. The analyses based on the AIC indicated that there is less support for the interacting ΛCDM model when compared to the ΛCDM model, while those based on the BIC indicated that there is strong evidence against it in favor of the ΛCDM model. Given the weak or almost non-existing support for the interacting ΛCDM model and bearing in mind Occam’s razor we are inclined to reject this model.

Recent astronomical observations have indicated that the Universe is in a phase of accelerated expansion. While there are many cosmological models which try to explain this phenomenon, we focus on the interacting ΛCDM model where an interaction between the darkenergy and dark matter sectors takes place. This model is compared to its simpler alternative - the ΛCDM model. To choose between these models the likelihood ratio test was applied as well as the model comparison methods (employing Occam's principle): the Akaike information criterion (AIC), the Bayesian information criterion (BIC) and the Bayesian evidence. Using the current astronomical data: type Ia supernova (Union2.1), h(z), baryon acoustic oscillation, the Alcock- Paczynski test, and the cosmic microwave background data, we evaluated both models. The analyses based on the AIC indicated that there is less support for the interacting ΛCDM model when compared to the ΛCDM model, while those based on the BIC indicated that there is strong evidence against it in favor of the ΛCDM model. Given the weak or almost non-existing support for the interacting ΛCDM model and bearing in mind Occam's razor we are inclined to reject this model. (orig.)

We calculate the gravitational memory effect when a spherically symmetric shell of energy passes through a spacetime region. In particular, this effect includes a longitudinal component, such that two radially separated geodesics pick up a relative velocity proportional to their separation. Such a measurement will allow us to obtain the total energy released by a supernova explosion in the form of neutrinos. We study the possibility to measure such an effect by space-based interferometers such as LISA and BBO, and also by astrophysical interferometers such as pulsar scintillometry.

The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over macroscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e., the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives darkenergy without "fine-tuning". Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonline...

A coupling between a light scalar field and neutrinos has been widely discussed as a mechanism for linking (time varying) neutrino masses and the present energy density and equation of state of darkenergy. However, it has been pointed out that the viability of this scenario in the non-relativistic neutrino regime is threatened by the strong growth of hydrodynamic perturbations associated with a negative adiabatic sound speed squared. In this paper we revisit the stability issue in the framework of linear perturbation theory in a model independent way. The criterion for the stability of a model is translated into a constraint on the scalar-neutrino coupling, which depends on the ratio of the energy densities in neutrinos and cold dark matter. We illustrate our results by providing meaningful examples both for stable and unstable models.

We demonstrate that a scalar field is unable to reverse its direction of motion while continuously exchanging energy with another fluid. If the rate of transfer is modulated by the scalar's acceleration, the field can undergo a rapid process of freezing, despite being displaced from the local minimum of its potential. This enables darkenergy to form from any potential, regardless of its shape. The field's equation of state mimicks that of a cosmological constant. We present a physically motivated realisation in the form of a derivative neutrino-majoron coupling. Coherent motions, which form only once the neutrinos become non-relativistic, could be responsible for instigating the freezing process. This would provide a natural resolution to the darkenergy coincidence problem, while avoiding the dynamical instabilities associated with mass-varying neutrino models. Finally we discuss possible means by which this model could be experimentally verified.

A coupling between a light scalar field and neutrinos has been widely discussed as a mechanism for linking (time varying) neutrino masses and the present energy density and equation of state of darkenergy. However, it has been pointed out that the viability of this scenario in the non-relativistic neutrino regime is threatened by the strong growth of hydrodynamic perturbations associated with a negative adiabatic sound speed squared. In this paper we revisit the stability issue in the framework of linear perturbation theory in a model independent way. The criterion for the stability of a model is translated into a constraint on the scalar-neutrino coupling, which depends on the ratio of the energy densities in neutrinos and cold dark matter. We illustrate our results by providing meaningful examples both for stable and unstable models. (orig.)

Full Text Available Darkenergy with negative pressure and positive energy density is believed to be responsible for the accelerated expansion of the universe. Quite a few theoretical models of darkenergy are based on tachyonic fields interacting with itself and normal (bradyonic matter. Here, we propose an experimental model of tachyonic darkenergy based on hyperbolic metamaterials. Wave equation describing propagation of extraordinary light inside hyperbolic metamaterials exhibits 2 + 1 dimensional Lorentz symmetry. The role of time in the corresponding effective 3D Minkowski spacetime is played by the spatial coordinate aligned with the optical axis of the metamaterial. Nonlinear optical Kerr effect bends this spacetime resulting in effective gravitational force between extraordinary photons. We demonstrate that this model has a self-interacting tachyonic sector having negative effective pressure and positive effective energy density. Moreover, a composite multilayer SiC-Si hyperbolic metamaterial exhibits closely separated tachyonic and bradyonic sectors in the long wavelength infrared range. This system may be used as a laboratory model of inflation and late time acceleration of the universe.

It has been shown in a companion paper that the late time acceleration of the universe can be accounted for by an extension of the QCD color to a $SU(3)$ invisible sector (IQCD). In this work we discuss a unified framework such the scale of dark chiral-breaking dictates both the accelerated expansion of the universe, and the origin of dark matter. We find that the strong and gravitational dynamics of dark quarks and gluons evolve to eventually form exotic dark stars. We discuss the dynamical complexity of these dark compact objects in light of dark big bang nucleosynthesis. We argue how IQCD favors a halo composed of very compact dark neutron stars, strange/quark stars and black holes, with masses $M_{MACHO}< 10^{-7}M_{\\odot}$. This avoids limit from MACHO and EROS collaborations as well as limit from clusters. We also discuss possible phenomenological implications in dark matter searches. We argue that darksupernovae and dark binaries can emit very peculiar gravitational waves signal testable by the LIGO...

@@ A conjecture on the origin of the darkenergy in our universe is proposed. The analysis indicates that the darkenergy may originate from the quantum fluctuations of space-time limited in our universe.

In this work, we have studied accretion of darkenergy (DE) onto Morris- Thorne wormhole with three different forms, namely, holographic darkenergy, holographic Ricci darkenergy and modified holographic Ricci darkenergy . Considering the scale factor in power-law form we have observed that as the holographic darkenergy accretes onto wormhole, the mass of the wormhole is decreasing. In the next phase we considered three parameterization schemes that are able to get hold of quintessence as well as phantom phases. Without any choice of scale factor we reconstructed Hubble parameter from conservation equation and darkenergy densities and subsequently got the mass of the wormhole separately for accretion of the three darkenergy candidates. It was observed that if these darkenergies accrete onto the wormhole, then for quintessence stage, wormhole mass decreases up to a certain finite value and then again increases to aggressively during phantom phase of the universe.

We extend the loop quantum cosmology matter bounce scenario in order to include a darkenergy era, which ends abruptly at a rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario," the Universe is contracting from an initial noncausal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, and thus the model is described by a darkenergy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the darkenergy era is quintessential as what follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the darkenergy era, a rip singularity exists, where the scale factor and Hubble rate diverge; however, the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, first that the ordinary loop quantum cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Second, the fact that both the pressure and the density become complex probably indicates that the description of the cosmic evolution within the theoretical context of loop quantum cosmology ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be rip singularity. We describe the qualitative features of the model, and we also investigate how this cosmology could be realized by a viscous fluid in the context of loop quantum cosmology. In addition to this, we show how this deformed model can be realized by a canonical scalar field filled Universe, in the context of loop quantum cosmology. Finally, we demonstrate how the model can be generated by a vacuum F (R ) gravity.

observations show that the temperature changes with radius are much steeper than predicted by the currently favoured models, indicating that most of the near-infrared emission emerges from hot material located very close to the star, that is, within one or two times the Earth-Sun distance (1-2 AU). This also implies that dust cannot exist so close to the star, since the strong energy radiated by the star heats and ultimately destroys the dust grains. ESO PR Photo 03/08 ESO PR Photo 03b/08 The Region Around MWC 147 "We have performed detailed numerical simulations to understand these observations and reached the conclusion that we observe not only the outer dust disc, but also measure strong emission from a hot inner gaseous disc. This suggests that the disc is not a passive one, simply reprocessing the light from the star," explained Kraus. "Instead, the disc is active, and we see the material, which is just transported from the outer disc parts towards the forming star." ESO PR Photo 03/08 ESO PR Photo 03c/08 Close-up on MWC 147 The best-fit model is that of a disc extending out to 100 AU, with the star increasing in mass at a rate of seven millionths of a solar mass per year. "Our study demonstrates the power of ESO's VLTI to probe the inner structure of discs around young stars and to reveal how stars reach their final mass," said Stefan Kraus. More Information The authors report their results in a paper in the Astrophysical Journal ("Detection of an inner gaseous component in a Herbig Be star accretion disk: Near- and mid-infrared spectro-interferometry and radiative transfer modeling of MWC 147", by Stefan Kraus, Thomas Preibisch, Keichii Ohnaka").

If darkenergy---which drives the accelerated expansion of the universe---consists of a new light scalar field, it might be detectable as a "fifth force" between normal-matter objects, in potential conflict with precision tests of gravity. There has, however, been much theoretical progress in developing theories with screening mechanisms, which can evade detection by suppressing forces in regions of high density, such as the laboratory. One prominent example is the chameleon field. We reduce the effect of this screening mechanism by probing the chameleon with individual atoms rather than bulk matter. Using a cesium matter-wave interferometer near a spherical mass in an ultra-high vacuum chamber, we constrain a wide class of dynamical darkenergy theories. Our experiment excludes a range of chameleon theories that reproduce the observed cosmic acceleration.

We study the singularity problem in teleparallel darkenergy models. A future singularity may occur due to the non-minimal coupling of the darkenergy scalar field to teleparallel gravity that effectively changes the gravitational coupling strength and can even make it diverge. This singularity may be avoided by a binding-type self-potential that keeps the scalar field away from the singularity point. For demonstration we analyze the model with a quadratic potential and show how the (non)occurrence of the singularity depends on the initial conditions and the steepness of the potential, both of which affect the competition between the self-interaction and the non-minimal coupling. To examine the capability of the binding-type potential to fit observational data and meanwhile to avoid the singularity, we perform the data fitting for this model and show that the observationally viable region up to the $3\\sigma$ confidence level is free of the future singularity.

We investigate the effects of negative pressure induced by darkenergy (cosmological constant or quintessence) on the dynamics at various astrophysical scales. Negative pressure induces a repulsive term (antigravity) in Newton's law which dominates on large scales. Assuming a value of the cosmological constant consistent with the recent SnIa data we determine the critical scale $r_c$ beyond which antigravity dominates the dynamics ($r_c \\sim 1Mpc $) and discuss some of the dynamical effects implied. We show that dynamically induced mass estimates on the scale of the Local Group and beyond are significantly modified due to negative pressure. We also briefly discuss possible dynamical tests (eg effects on local Hubble flow) that can be applied on relatively small scales (a few $Mpc$) to determine the density and equation of state of darkenergy.

We investigate the effects of negative pressure induced by darkenergy (cosmological constant or quintessence) on the dynamics at various astrophysical scales. Negative pressure induces a repulsive term (antigravity) in Newton's law which dominates on large scales. Assuming a value of the cosmological constant consistent with the recent SnIa data we determine the critical scale $r_c$ beyond which antigravity dominates the dynamics ($r_c \\sim 1Mpc $) and discuss some of the dynamical effects implied. We show that dynamically induced mass estimates on the scale of the Local Group and beyond are significantly modified due to negative pressure. We also briefly discuss possible dynamical tests (eg effects on local Hubble flow) that can be applied on relatively small scales (a few $Mpc$) to determine the density and equation of state of darkenergy.

We confront two types of phantom darkenergy potential with observational data. The models we consider are the power-law potential, $V\\propto {\\phi}^{\\mu}$, and the exponential potential, $V\\propto \\exp({\\lambda}{\\phi}/{M_P})$. We fit the models to the latest observations from SN-Ia, CMB and BAO, and obtain tight constraints on parameter spaces. Furthermore, we apply the goodness-of-fit and the information criteria to compare the fitting results from phantom models with that from the cosmological constant and the quintessence models presented in our previous work. The results show that the cosmological constant is statistically most preferred, while the phantom darkenergy fits slightly better than the quintessence does.

We present a formalism for the numerical implementation of general theories of darkenergy, combining the computational simplicity of the equation of state for perturbations approach with the generality of the effective field theory approach. An effective fluid description is employed, based on a general action describing single-scalar field models. The formalism is developed from first principles, and constructed keeping the goal of a simple implementation into CAMB in mind. Benefits of this approach include its straightforward implementation, the generality of the underlying theory, the fact that the evolved variables are physical quantities, and that model-independent phenomenological descriptions may be straightforwardly investigated. We hope this formulation will provide a powerful tool for the comparison of theoretical models of darkenergy with observational data.

Theories with a time dependent Newton's constant admit two natural measures of time : atomic and astronomical. Temporal parametrisation by SL(2, R) transformations gives rise to an equivalence between theories with different time dependence's, including the special Case of no time dependence, a fact noticed by Mestschersky, Vinti and by Lynden-Bell. I point out that theories with time dependent darkenergy densities admit three natural measures of time : atomic and astronomical and de Sitter related by temporal re-parametrizations and I extend Mestschersky-Vinti-Lynden-Bell's result to cover this more general situation. I find a consequent equivalence between theories in which the density of darkenergy is constant in time and in which it varies with time. Strikingly a time dependent cosmological constant changes by the addition of a Schwarzian derivative term unless the temporal reparameterization belongs to SL(2, R). In General Relativity one may introduce a Schwarzian tensor to investigate how the notion o...

We investigate a possible connection between the suppression of the power at low multipoles in the CMB spectrum and the late time acceleration. We show that, assuming a cosmic IR/UV duality between the UV cutoff and a global infrared cutoff given by the size of the future event horizon, the equat......We investigate a possible connection between the suppression of the power at low multipoles in the CMB spectrum and the late time acceleration. We show that, assuming a cosmic IR/UV duality between the UV cutoff and a global infrared cutoff given by the size of the future event horizon......, the equation of state of the darkenergy can be related to the apparent cutoff in the CMB spectrum. The present limits on the equation of state of darkenergy are shown to imply an IR cutoff in the CMB multipole interval of 9>l>8.5....

In the search for the nature of darkenergy most cosmological probes measure simple functions of the expansion rate. While powerful, these all involve roughly the same dependence on the darkenergy equation of state parameters, with anticorrelation between its present value w{sub 0} and time variation w{sub a}. Quantities that have instead positive correlation and so a sensitivity direction largely orthogonal to, e.g., distance probes offer the hope of achieving tight constraints through complementarity. Such quantities are found in strong gravitational lensing observations of image separations and time delays. While degeneracy between cosmological parameters prevents full complementarity, strong lensing measurements to 1 percent accuracy can improve equation of state characterization by 15-50 percent. Next generation surveys should provide data on roughly 105 lens systems, though systematic errors will remain challenging.

@@ We discuss the possibility that the existence of darkenergy may be due to the presence ofa spin zero field φ(x), either elementary or composite. In the presence of other matter field, the transformation φ(x) → φ(x) + constant can generate a negative pressure, like the cosmological constant. In this picture, our universe can be thought as a very large bag, similar to the much smaller MIT bag model for a single nucleon.

The thorny issue of relating information theory to cosmology is here addressed by assuming a possible connection between quantum entanglement measures and observable universe. In particular, we propose a cosmological toy model, where the equation of state of the cosmological fluid, which drives the today observed cosmic acceleration, can be inferred from quantum entanglement between different cosmological epochs. In such a way the dynamical darkenergy results as byproduct of quantum entanglement.

Galileon models are among the most appealing candidates for DarkEnergy. The reason is twofold: classically, they provide a tracking solution leading to an almost DeSitter space starting from very generic initial conditions in the deep radiation era. The second reason is the standard lore that Galileons are quantum mechanically stable. The latter property is certainly true in flat space-time, thanks to the non-renormalisation theorems of Galilean coupling constants. However, in a cosmological background, we show that quantum effects might dominate the classical trajectory. Assuming the radiation era to last at least up to the electroweak phase transition, the trajectory with initial conditions sitting on the tracker is ruled out. On the other hand, it is always possible to find a sub-space of initial conditions such that the darkenergy solution approaches stably the tracker at late times. Fixing the value of initial conditions that best fit current data, and assuming that the Galileon effective theory is valid up to the beginning of the radiation epoch, we found that the reheating temperature of the universe cannot be larger than 108 GeV. Reversing the argument, if darkenergy will turn out to be in form of Galileons, the bounds by EUCLID on the initial conditions for these models will also be a bound on the reheating temperature of our Universe.

Strong lensing gravitational time delays are a powerful and cost effective probe of darkenergy. Recent studies have shown that a single lens can provide a distance measurement with 6-7 % accuracy (including random and systematic uncertainties), provided sufficient data are available to determine the time delay and reconstruct the gravitational potential of the deflector. Gravitational-time delays are a low redshift (z~0-2) probe and thus allow one to break degeneracies in the interpretation of data from higher-redshift probes like the cosmic microwave background in terms of the darkenergy equation of state. Current studies are limited by the size of the sample of known lensed quasars, but this situation is about to change. Even in this decade, wide field imaging surveys are likely to discover thousands of lensed quasars, enabling the targeted study of ~100 of these systems and resulting in substantial gains in the darkenergy figure of merit. In the next decade, a further order of magnitude improvement will...

The presence of darkenergy in the Universe is inferred directly from the accelerated expansion of the Universe, and indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Darkenergy contributes about 2/3 of the critical density, is very smoothly distributed, and has large negative pressure. Its nature is very much unknown. Most of its discernible consequences follow from its effect on evolution of the expansion rate of the Universe, which in turn affects the growth of density perturbations and the age of the Universe, and can be probed by the classical kinematic cosmological tests. Absent a compelling theoretical model (or even a class of models), we describe the darkenergy by an effective equation-of-state w=p_X/\\rho_X which is allowed to vary with time. We describe and compare different approaches for determining w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy, focusing particular attention on the use of a sample of s...

The presence of darkenergy in the Universe is inferred directly from the accelerated expansion of the Universe, and indirectly, from measurements of cosmic microwave background (CMB) anisotropy. Darkenergy contributes about 2/3 of the critical density, is very smoothly distributed, and has large negative pressure. Its nature is very much unknown. Most of its discernible consequences follow from its effect on evolution of the expansion rate of the Universe, which in turn affects the growth of density perturbations and the age of the Universe, and can be probed by the classical kinematic cosmological tests. Absent a compelling theoretical model (or even a class of models), we describe darkenergy by an effective equation of state w=p_X/rho_X which is allowed to vary with time. We describe and compare different approaches for determining w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies and clusters, and CMB anisotropy, focusing particular attention on the use of a sample of severa...

The darkenergy is a fundamental constitution of our universe, its role in the cosmological field equation should just like the gravity. Here we construct a darkenergy and gravity coupling (DEMC) model of cosmology in a way that gravity and darkenergy are introduced into the cosmological field equation in parallel to each other from the beginning. The DEMC universe possesses a composite symmetry constituted from the global Galileo invariance and local Lorentz invariance. The observed evolution trend of expansion rate at redshift z>1 is in tension with the standard LCDM model, but can be well predicted from measurements for only near epoch by the DEMC model. The so far most precise measured expansion rate at high z is quite a bit slower than the expectation from LCDM, but remarkably consistent with that from DEMC. It is hopeful that the DEMC scenario can also help to solve existed challenges to cosmology: large scale anomalies in CMB maps and large structures with dimension up to about 10^3 Mpc of a quasar g...

Inspired by the multiverse scenario, we study a heterotic darkenergy model in which there are two parts, the first being the cosmological constant and the second being the holographic darkenergy, thus this model is named the ΛHDE model. By studying the ΛHDE model theoretically, we find that the parameters d and Ωhde are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the ΛHDE model by using the recent observational data. We find the model yields χ2min=426.27 when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant ΛCDM model (431.35). At 68.3% CL, we obtain -0.07dark energy and cosmological constant components in the ΛHDE model.

By detecting redshift drift in the spectra of Lyman-$\\alpha$ forest of distant quasars, Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the "redshift desert" of $2 \\lesssim z \\lesssim5$. Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of SL test signal by a CODEX-like spectrograph for constraining interacting darkenergy. Four typical interacting darkenergy models are considered: (\\romannumeral1) $Q=\\gamma H\\rho_c$, (\\romannumeral2) $Q=\\gamma H\\rho_{de}$, (\\romannumeral3) $Q=\\gamma H_0\\rho_c$, and (\\romannumeral4) $Q=\\gamma H_0\\rho_{de}$. The results show that for all the considered interacting darkenergy models, relative to the current joint SN+BAO+CMB+$H_0$ observations, the constraints on $\\Omega_m$ and $H_0$ would be improved by about 60\\% and 30--40\\%, while the constraints on $w$ and $\\gamma$ would be slightly improved, with a 30-y...

Full Text Available The ΛCDM paradigm, characterised by a constant equation of state w = − 1 for darkenergy, is the model that better fits observations. However, the same observations strongly support the possibility of a darkenergy content where the corresponding equation of state is close to but slightly smaller than − 1 . In this regard, we focus on three different models where the darkenergy content is described by a perfect fluid with an equation of state w ≲ − 1 which can evolve or not. The three proposals show very similar behaviour at present, while the asymptotic evolution of each model drives the Universe to different abrupt events known as (i Big Rip; (ii Little Rip (LR; and (iii Little Sibling of the Big Rip. With the aim of comparing these models and finding possible imprints in their predicted matter distribution, we compute the matter power spectrum and the growth rate f σ 8 . We conclude that the model which induces a LR seems to be favoured by observations.

In this Letter, we consider the possibility of reconciling metric theories of gravitation with a violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein's equation. We specifically investigate two potential sources of energy nonconservation-nonunitary modifications of quantum mechanics and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale-and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale.

In this Letter, we consider the possibility of reconciling metric theories of gravitation with a violation of the conservation of energy-momentum. Under some circumstances, this can be achieved in the context of unimodular gravity, and it leads to the emergence of an effective cosmological constant in Einstein's equation. We specifically investigate two potential sources of energy nonconservation—nonunitary modifications of quantum mechanics and phenomenological models motivated by quantum gravity theories with spacetime discreteness at the Planck scale—and show that such locally negligible phenomena can nevertheless become relevant at the cosmological scale.

A new interpretation of dark matter observations via gravitational lensing through galaxy clusters is proposed. Gravitational lensing studies of SDSS J1004+4112 by Williams and Saha (astro-ph/0412445) indicate that any dark matter contribution to lensing is smoothly distributed in space. All particle theories (i.e WIMPs) which propose to explain dark matter inevitably yield gravitational clumping. Note that string theory requires that matter at radii, R, less than the Planck scale, α', is equivalent to matter at distance D=α'/R. The proposed interpretation involves antimatter existing within anti-deSitter spaces to explain the unexpected smoothness. This proposal asserts that a (non-Hawking) black hole exists with an AdS space at its singularity. Antimatter interactions also explain Galactic Annihilation Fountain(s) and similar observed phenomena. Non-temporal matter is thereby defined as matter which exists in 4-space, either advanced or retarded wrt the present. A `radical' form of cosmology is then developed in which the curvature tensor of Einstein's general relativity is treated as complex. FRW cosmology plus dark matter and energy results. Theories regarding the black hole ``end state'' and Seiberg's chronology protection lend support to this approach. Previous work (http://www-astro-theory.fnal.gov/Conferences/cosmo02/poster/lundberg.pdfhttp://www-astro-theory.fnal.gov/Conferences/cosmo02/poster/lundberg.pdf) to establish the architecture of a comprehensive theory is thus modified.

We re-analyze the possibility of large scale dark (bulk) flow with respect the the CMB background based upon the redshift-distance relation for Type Ia Supernovae (SN Ia). We have made a Markov chain Monte Carlo analysis in redshift bins for $z 0.05$ using both Union.2.1 and SDSS-II data sets. We have also made studies based upon simulated data in which a bulk flow is imposed to determine whether the difficulty in detecting a bulk flow at high redshift is due to uncertainty in the redshift-distance relation, confusion with peculiar velocities, or the absence of a bulk flow. With the Union2.1 data set, we find a bulk flow velocity of $v_{\\text{bf}} = 270 \\pm 50 \\text{ km s}^{-1}$ in the direction of galactic coordinates, $(l,b) = (295 \\pm 30, 10 \\pm 5)^{\\circ}$, consistent with previous analyses. While in the redshift bin $z > 0.05$ we find only marginal evidence for a bulk flow velocity of $v_{\\text{bf}} = 1000 \\pm 600 \\text{ km s}^{-1}$ in the direction of galactic coordinates $(l,b) = (120 \\pm 80, -5 \\pm 3...

The physical relation between the properties of Type Ia supernovae and their host galaxies is investigated. Such supernovae are used to constrain the properties of darkenergy, making it crucial to understand their physical properties and to check for systematic effects relating to the stellar populations of the progenitor stars from which these supernovae arose. This grant found strong evidence for two distinct populations of supernovae, and correlations between the progenitor stellar populations and the nature of the supernova light curves.

The coalescence of a binary neutron star pair is expected to produce gravitational waves (GW) and electromagnetic radiation, both of which may be detectable with currently available instruments. We describe a search for a predicted r-process optical transient from these mergers, dubbed the “kilonova” (KN), using griz broadband data from the DarkEnergy Survey Supernova Program (DES-SN). Some models predict KNe to be redder, shorter-lived, and dimmer than supernovae (SNe), but the event rate of KNe is poorly constrained. We simulate KN and SN light curves with the Monte-Carlo simulation code SNANA to optimize selection requirements, determine search efficiency, and predict SN backgrounds. Our analysis of the first two seasons of DES-SN data results in 0 events, and is consistent with our prediction of 1.1 ± 0.2 background events based on simulations of SNe. From our prediction, there is a 33% chance of finding 0 events in the data. Assuming no underlying galaxy flux, our search sets 90% upper limits on the KN volumetric rate of 1.0 x10$^{7}$ Gpc$-$3 yr$-$1 for the dimmest KN model we consider (peak i-band absolute magnitude ${M}_{i}=-11.4$ mag) and 2.4x10$^{4}$ Gpc$-$3 yr$-$1 for the brightest (${M}_{i}=-16.2$ mag). Accounting for anomalous subtraction artifacts on bright galaxies, these limits are ~3 times higher. This analysis is the first untriggered optical KN search and informs selection requirements and strategies for future KN searches. Our upper limits on the KN rate are consistent with those measured by GW and gamma-ray burst searches.

The coalescence of a binary neutron star pair is expected to produce gravitational waves (GW) and electromagnetic radiation, both of which may be detectable with currently available instruments. We describe a search for a predicted r-process optical transient from these mergers, dubbed the “kilonova” (KN), using griz broadband data from the DarkEnergy Survey Supernova Program (DES-SN). Some models predict KNe to be redder, shorter-lived, and dimmer than supernovae (SNe), but the event rate of KNe is poorly constrained. We simulate KN and SN light curves with the Monte-Carlo simulation code SNANA to optimize selection requirements, determine search efficiency, and predict SN backgrounds. Our analysis of the first two seasons of DES-SN data results in 0 events, and is consistent with our prediction of 1.1 ± 0.2 background events based on simulations of SNe. From our prediction, there is a 33% chance of finding 0 events in the data. Assuming no underlying galaxy flux, our search sets 90% upper limits on the KN volumetric rate of 1.0 × {10}7 Gpc‑3 yr‑1 for the dimmest KN model we consider (peak i-band absolute magnitude {M}i=-11.4 mag) and 2.4 × {10}4 Gpc‑3 yr‑1 for the brightest ({M}i=-16.2 mag). Accounting for anomalous subtraction artifacts on bright galaxies, these limits are ∼3 times higher. This analysis is the first untriggered optical KN search and informs selection requirements and strategies for future KN searches. Our upper limits on the KN rate are consistent with those measured by GW and gamma-ray burst searches.

In the context of $f(\\mathcal{R})$ gravity, darkenergy is a geometrical fluid with negative equation of state. Since the function $f(\\mathcal{R})$ is not known \\emph{a priori}, the need of a model independent reconstruction of its shape represents a relevant technique to determine which $f(\\mathcal{R})$ model is really favored with respect to others. To this aim, we relate cosmography to a generic $f(\\mathcal R)$ and its derivatives in order to provide a model independent investigation at redshift $z \\sim 0$. Our analysis is based on the use of three different cosmological distance definitions, in order to alleviate the duality problem, i.e. the problem of which cosmological distance to use with specific cosmic data sets. We therefore consider the luminosity, $d_L$, flux, $d_F$, and angular, $d_A$, distances and we find numerical constraints by the Union 2.1 supernovae compilation and measurement of baryonic acoustic oscillations, at $z_{BAO}=0.35$. We notice that all distances reduce to the same expression, i.e. $d_{L;F;A}\\sim\\frac{1}{\\mathcal H_0}z$, at first order. Thus, to fix the cosmographic series of observables, we impose the initial value of $H_0$ by fitting $\\mathcal H_0$ through supernovae only, in the redshift regime $z1$. Finally, we infer the functional form of $f(\\mathcal{R})$ by means of a truncated polynomial approximation, in terms of fourth order scale factor $a(t)$.

The existence of dark matter and darkenergy in cosmology is implied by various observations, however, they are still unclear because they have not been directly detected. In this Letter, an unified model of darkenergy and dark matter that can explain the evolution history of the Universe later than inflationary era, the time evolution of the growth rate function of the matter density contrast, the flat rotation curves of the spiral galaxies, and the gravitational experiments in the solar sy...

Full Text Available Considering the cosmic fluid as a quasi-static thermodynamic system, the status of the generalized second law of thermodynamics is investigated and the valid range of the equation of state parameter is derived for a few important cosmological models. Our study shows that the satisfaction of the laws of thermodynamics in these cosmological models requires the existence of some kind of energy in our universe with ωdark energy component, or equivalently modified gravity theory, is unavoidable if the cosmological model is to approach thermal equilibrium in late times.

In order to study if the bulk viscosity may induce a big rip singularity on the flat FRW cosmologies, we investigate dissipative processes in the universe within the framework of the standard Eckart theory of relativistic irreversible thermodynamics, and in the full causal Israel-Stewart-Hiscock theory. We have found cosmological solutions which exhibit, under certain constraints, a big rip singularity. We show that the negative pressure generated by the bulk viscosity cannot avoid that the darkenergy of the universe to be phantom energy.

In this paper, we investigate the statefinder, the deceleration and equation of state parameters when universe is composed of generalized holographic darkenergy or generalized Ricci darkenergy for Bianchi I universe model. These parameters are found for both interacting as well as non-interacting scenarios of generalized holographic or generalized Ricci darkenergy with dark matter and generalized Chaplygin gas. We explore these parameters graphically for different situations. It is concluded that these models represent accelerated expansion of the universe.

The dynamical analysis for coupled darkenergy with dark matter is presented, where a complex scalar field is taken into account and it is considered in the presence of a barothropic fluid. We consider three dark-energy candidates: quintessence, phantom, and tachyon. The critical points are found and their stabilities analyzed, leading to the three cosmological eras (radiation, matter, and darkenergy), for a generic potential. The results presented here extend the previous analyses found in the literature. (orig.)

We investigate several aspects of dynamical darkenergy in the framework of scalar-tensor theories of gravity. We provide a classification of scalar-tensor coupling functions admitting cosmological scaling solutions. In particular, we recover that Brans-Dicke theory with inverse power-law potential allows for a sequence of background dominated scaling regime and scalar field dominated, accelerated expansion. Furthermore, we compare minimally and non-minimally coupled models, with respect to the small redshift evolution of the darkenergy equation of state. We discuss the possibility to discriminate between different models by a reconstruction of the equation-of-state parameter from available observational data. The non-minimal coupling characterizing scalar-tensor models can - in specific cases - alleviate fine tuning problems, which appear if (minimally coupled) quintessence is required to mimic a cosmological constant. Finally, we perform a phase-space analysis of a family of biscalar-tensor models characterized by a specific type of {sigma}-model metric, including two examples from recent literature. In particular, we generalize an axion-dilaton model of Sonner and Townsend, incorporating a perfect fluid background consisting of (dark) matter and radiation. (orig.)

We study a correspondence between f(R) model of gravity in the Jordan frame and a phenomenological kind of darkenergy (DE), which is known as QCD ghost DE. Since this kind of DE is not stable in the context of Einsteinian theory of gravity and Brans-Dicke model of gravity, we consider two kinds of correspondence between modified gravity and DE. By studding the dynamical evolution of model and finding relevant quantities such as, equation of state parameter, deceleration parameter, dimensionless density parameter, we show that the model can describe the present Universe and also the EoS parameter can cross the phantom divide line without needs to any kinetic energy with negative sign. Furthermore, by obtaining the adiabatic squared sound speed of the model for different cases of interaction, we show that this model is stable. Finally, we fit this model with supernova observational data in a noninteraction case and we find the best values of parameter at 1σ confidence interval as; f0 = 0.958+0.07-0.25, β = -0, 256+0.2-0.1 and {Ω }m0 = 0.23+0.3-0.15. These best-fit values show that DE equation of state parameter, ωd0, can cross the phantom divide line at the present time.

We show that the darkenergy (DE) effects can be modeled by using an Ising perfect fluid with network interactions, whose low redshift equation of state (EoS), i.e. ω0, becomes ω0 = -1 as in the ΛCDM model. In our picture, DE is characterized by a barotropic fluid on a lattice in the equilibrium configuration. Thus, mimicking the spin interaction by replacing the spin variable with an occupational number, the pressure naturally becomes negative. We find that the corresponding EoS mimics the effects of a variable DE term, whose limiting case reduces to the cosmological constant Λ. This permits us to avoid the introduction of a vacuum energy as DE source by hand, alleviating the coincidence and fine tuning problems. We find fairly good cosmological constraints, by performing three tests with supernovae Ia (SNeIa), baryonic acoustic oscillation (BAO) and cosmic microwave background (CMB) measurements. Finally, we perform the Akaike information criterion (AIC) and Bayesian information criterion (BIC) selection criteria, showing that our model is statistically favored with respect to the Chevallier-Polarsky-Linder (CPL) parametrization.

Full text: The study of gravastars, in general, has considered these objects embedded in a Schwarzschild spacetime. However, taking the point of view that the universe must be fulfilled by a considerable amount of darkenergy, it is very important to investigate its influence in the gravastar stability and in the possible dynamical evolution. In a first step, we have considered the de Sitter-Schwarzschild exterior spacetime, in order to introduce a positive cosmological constant, which has been suggested as a darkenergy candidate. Then, with this purpose, we constructed three-layer dynamical models, which consists of an internal anisotropic darkenergy fluid, a dynamical infinitely thin shell of perfect fluid with the equation of state p = (1 - γ)σ, and an external de Sitter- Schwarzschild spacetime. The present work allows to confirm one of the conclusion of one of the our previous work, that is, the sign of the difference between the pressures (radial and tangential) affects the conditions of the formation of the gravastar and black hole when the interior fluid of prototype gravastars are anisotropic, even when combined with an external cosmological constant. We have shown explicitly that the final output can be a black hole, a 'bounded excursion' stable gravastar depending on the total mass m of the system, the cosmological constant L{sub e}, the parameter ω, the constant a, the parameter γ and the initial position R{sub 0} of the dynamical shell. Another interesting result is that we can have black hole and stable gravastar formation even with an interior and a shell constituted of dark and repulsive darkenergy. We also would like to point out the significant influence of the presence of the exterior cosmological constant to formation of this kind of structure, since there are some cases where we have a stable gravastar (for Λ 0) or none structure (for Λ > 0). Still more interesting is a case, where for small radius of the shell, we have

We analyse three cosmological scenarios with interaction in the dark sector, which are particular cases of a general expression for the energy flux from vacuum to matter. In the first case the interaction leads to a transition from an unstable de Sitter phase to a radiation dominated universe, avoiding in this way the initial singularity. In the second case the interaction gives rise to a slow-roll power-law inflation. Finally, the third scenario is a concordance model for the late-time universe, with the vacuum term decaying into cold dark matter. We identify the physics behind these forms of interaction and show that they can be described as particular types of the modified Chaplygin gas.

The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence of an unidentified "darkenergy", or cosmological constant, devoid of any physical meaning. While this standard cosmology seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that the Local Void could host an amount of antimatter ($\\sim5\\times10^{15}\\,M_\\odot$) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity field produced by this "dark repulsor" can explain the anomalous motion of the Local Sheet away from the Local Void, as well as several other properties of nearby galaxies that seem to require vo...

If darkenergy is a light scalar field, it might interact with normal matter. The interactions, however, are suppressed in some leading models, which are thus compatible with current cosmological observations as well as solar-system and laboratory studies. Such suppression typically relies on the scalar's interaction with macroscopic amounts of ordinary matter, but can be bypassed by studying the interaction with individual particles. Using an atom interferometer, we have placed tight constraints on so-called chameleon models, ruling out interaction parameters βM > 4 ×104 . This limit is improved by 2.5 orders of magnitude relative to previous experiments. We have already increased the sensitivity of our interferometer hundredfold and are expecting a new constraint soon. Purpose-built experiments in the lab or on the international space station will completely close the gap and rule out out chameleons and other theories, such as axions, dark photons, symmetrons or f (R) gravity.

We construct a multimetric gravity theory containing N >= 3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector, and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N = 2 cannot be extended beyond the bimetric case. We apply our theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way darkenergy can be explained simply by dark copies of the well-understood standard model.

We construct a multimetric gravity theory containing N≥3 copies of standard model matter and a corresponding number of metrics. In the Newtonian limit, this theory generates attractive gravitational forces within each matter sector and repulsive forces of the same strength between matter from different sectors. This result demonstrates that the recently proven no-go theorem that forbids gravity theories of this type in N=2 cannot be extended beyond the bimetric case. We apply our theory to cosmology and show that the repulsion between different types of matter may induce the observed accelerating expansion of the universe. In this way darkenergy can be explained simply by dark copies of the well-understood standard model.

The gravitational collapse of a spherically symmetric cloud, made of both dark matter, $\\rho_{DM}$, and darkenergy, $p = w\\rho, (w < -1/3)$, is studied. It is found that when only darkenergy is present, black holes can never be formed. When both of them are present, balck holes can be formed, due to the condensation of the dark matter. Initially the dark matter may not play an important role, but, as time increases, it will dominate the collapse and finally leads to formation of black holes. This result remains true even when the interaction between the dark matter and darkenergy does not vanish. When $w < -1$ (phantoms), some models can also be interpreted as representing the death of a white hole that ejects both dark matter and phantoms. The ejected matter re-collapses to form a black hole.

Core-collapse supernovae play a key role in many of astrophysical processes, but the details of how these explosive events work remain elusive. Many questions about the CCSN explosion mechanism and progenitor stars could be answered by either detecting very-low-energysupernovae (VLE SNe) or alternately placing a tight upper bound on their fraction of the CCSN population. However, VLE SNe are by definition dim events. Many VLE SNe result from the failure of the standard CCSN explosion mechanism, meaning that any observable signature must be created by secondary processes either before or during the collapse. In this dissertation I examine alternate means of producing transients in otherwise-failed CCSNe and consider the use of shock breakout flashes to both detect VLE SNe and retrieve progenitor star information. I begin by simulating neutrino-mediated mass loss in CCSNe progenitors to show that a dim, unusual, but still observable transient can be produced. I then simulate shock breakout flashes in VLE SNe for both the purposes of detection as well as extracting information about the exploding star. I discuss particular challenges of modeling shock breakout at low energies and behaviors unique to this regime, in particular the behavior of the spectral temperature. All simulations in this dissertation were done with the CASTRO radiation-hydrodynamic code.

Many darkenergy models fail to pass the cosmic age test via the old quasar APM 08279+5255 at redshift $z=3.91$, even the $\\Lambda$CDM model and the holographic darkenergy model are not exception. In this paper, we focus on the topic of age problem in the new agegraphic darkenergy (NADE) model. We determine the age of the universe in the NADE model by using the fitting result of observational data including type Ia supernovae (SNIa), baryon acoustic oscillation (BAO) and cosmic microwave background (CMB). It is shown that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255. In order to overcome such a difficulty, we consider the possible interaction between darkenergy and matter. We show that the old quasar APM 08279+5255 at redshift $z=3.91$ can be successfully accommodated in the interacting new agegraphic darkenergy (INADE) model at $2\\sigma$ level under the current observational constraints.

Full Text Available . The postulate of a finite vacuum/darkenergy density � is thus a natural starting point in cosmology and QFT. Within the theoretical framework developed in this chapter supernovae data can be used to establish the value of this dimensionfull parameter... conservation is broken. Lord Kelvin disagreed but was unable to give the right explanation. Then Rutherford in 1903 suggested that radioactivity is fed by an internal energy source inherent in the atom, and this picture was subsequently developed to a more...

We consider the hypothesis that the dark matter consists of ultra-light bosons residing in the state of a Bose-Einstein condensate, which behaves as a single coherent wave rather than as individual particles. In galaxies, spatial distribution of scalar field dark matter can be described by the relativistic Klein-Gordon equation on a background space-time with Schwarzschild metric. In such a setup, the equation of state of scalar field dark matter is found to be changing along with galactocent...

The well-known hierarchy between the Planck scale (~10^{19}GeV) and the TeV scale, namely a ratio of ~10^{16} between the two, is coincidentally repeated in a inverted order between the TeV scale and the darkenergy scale at \\~10^{-3}eV implied by the observations. We argue that this is not a numerical coincidence. The same brane-world setups to address the first hierarchy problem may also in principle address this second hierarchy issue. Specifically, we consider supersymmetry in the bulk and its breaking on the brane and resort to the Casimir energy induced by the bulk graviton-gravitino mass-shift on the brane as the darkenergy. For the ADD model we found that our notion is sensible only if the number of extra dimension n=2. We extend our study to the Randall-Sundrum model. Invoking the chirality-flip on the boundaries for SUSY-breaking, the zero-mode gravitino contribution to the Casimir energy does give rise to the double hierarchy. Unfortunately since the higher Kaluza-Klein modes acquire relative mass...

In this paper, we organize a look to nonlinear interacting Ghost darkenergy cosmology involving a discussion on the thermodynamics of the Ghost darkenergy, when the universe is bounded via the Hubble horizon. One of the ways to study a darkenergy model, is to reconstruct thermodynamics of it. Ghost darkenergy is one of the models of the darkenergy which has an explicitly given energy density as a function of the Hubble parameter. There is an active discussion towards various cosmological scenarios, where the Ghost darkenergy interacts with the pressureless cold dark matter (CDM). Recently, various models of the varying Ghost darkenergy has been suggested, too. To have a comprehensive understanding of suggested models, we will discuss behavior of the cosmological parameters on parameter-redshift z plane. Some discussion on Om and statefinder hierarchy analysis of these models is presented. Moreover, up to our knowledge, suggested forms of interaction between the Ghost darkenergy and cold dark matter (CDM) are new, therefore, within obtained results, we provide new contribution to previously discussed models available in the literature. Our study demonstrates that the forms of the interactions considered in the Ghost darkenergy cosmology are not exotic and the justification of this is due to the recent observational data.

By detecting redshift drift in the spectra of the Lyman-α forest of distant quasars, the Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the ''redshift desert'' of 2 dark energy. Four typical interacting darkenergy models are considered: (i) Q = γHρ{sub c}, (ii) Q = γHρ{sub de}, (iii) Q = γH{sub 0}ρ{sub c}, and (iv) Q = γH{sub 0}ρ{sub de}. The results show that for all the considered interacting darkenergy models, relative to the current joint SN + BAO + CMB + H{sub 0} observations, the constraints on Ω{sub m} and H{sub 0} would be improved by about 60 and 30-40 %, while the constraints on w and γ would be slightly improved, with a 30-year observation of the SL test. We also explore the impact of the SL test on future joint geometric observations. In this analysis, we take the model with Q = γHρ{sub c} as an example, and we simulate future SN and BAO data based on the space-based project WFIRST. We find that with the future geometric constraints, the redshift drift observations would help break the geometric degeneracies in a meaningful way, thus the measurement precisions of Ω{sub m}, H{sub 0}, w, and γ could be substantially improved using future probes. (orig.)

Full Text Available This paper aims to introduce a new parameterisation for the coupling Q in interacting dark matter and darkenergy models by connecting said models with the Continuous Tower of Scalar Fields model. Based upon the existence of a dark matter and a darkenergy sectors in the Continuous Tower of Scalar Fields, a simplification is considered for the evolution of a single scalar field from the tower, validated in this paper. This allows for the results obtained with the Continuous Tower of Scalar Fields model to match those of an interacting dark matter–darkenergy system, considering that the energy transferred from one fluid to the other is given by the energy of the scalar fields that start oscillating at a given time, rather than considering that the energy transference depends on properties of the whole fluids that are interacting.

The Sandage-Loeb (SL) test is a unique method to probe darkenergy in the "redshift desert" of $2\\lesssim z\\lesssim 5$, and thus it provides an important supplement to the other darkenergy probes. Therefore, it is of great importance to quantify how the future SL test data impact on the darkenergy constraints. To avoid the potential inconsistency in data, we use the best-fitting model based on the other geometric measurements as the fiducial model to produce 30 mock SL test data. The 10-yr, 20-yr, and 30-yr observations of SL test are analyzed and compared in detail. We show that compared to the current combined data of type Ia supernovae, baryon acoustic oscillation, cosmic microwave background, and Hubble constant, the 30-yr observation of SL test could improve the constraint on $\\Omega_m$ by about $80%$ and the constraint on $w$ by about $25%$. Furthermore, the SL test can also improve the measurement of the possible direct interaction between darkenergy and dark matter. We show that the SL test 30-yr d...

In this work we investigate if a small fraction of quarks and gluons, which escaped hadronization and survived as a uniformly spread perfect fluid, can play the role of both dark matter and darkenergy. This fluid, as developed in \\citep{Brilenkov}, is characterized by two main parameters: $\\beta$, related to the amount of quarks and gluons which act as dark matter; and $\\gamma$, acting as the cosmological constant. We explore the feasibility of this model at cosmological scales using data from type Ia Supernovae (SNeIa), Long Gamma-Ray Bursts (LGRB) and direct observational Hubble data. We find that: (i) in general, $\\beta$ cannot be constrained by SNeIa data nor by LGRB or H(z) data; (ii) $\\gamma$ can be constrained quite well by all three data sets, contributing with $\\approx78\\%$ to the energy-matter content; (iii) when a strong prior on (only) baryonic matter is assumed, the two parameters of the model are constrained successfully.

From measurements of the cosmic microwave background (CMB), the effective number of neutrino is found to be close to the standard model value Neff = 3.046 for the \\LambdaCDM cosmology. One can obtain the same CMB angular power spectrum as that of \\LambdaCDM for the different value of Neff by using the different darkenergy model (i.e. for the different value of w). This degeneracy between Neff and w in CMB can be broken from future galaxy survey using the matter power spectrum.

The American Physical Society's Division of Particles and Fields initiated a long-term planning exercise over 2012-13, with the goal of developing the community's long term aspirations. The sub-group "DarkEnergy and CMB" prepared a series of papers explaining and highlighting the physics that will be studied with large galaxy surveys and cosmic microwave background experiments. This paper summarizes the findings of the other papers, all of which have been submitted jointly to the arXiv.

We explore the possibility that a CP violating phase of the neutrino mass matrix is promoted to a pseudo-Goldstone-boson field and is identified as the quintessence field for DarkEnergy. By requiring that the quintessence potential be calculable from a Lagrangian, and that the extreme flatness of the potential be stable under radiative corrections, we are led to an essentially unique model. Lepton number is violated only by Majorana masses of light, right-handed neutrinos, comparable to the Dirac masses that mix right- with left-handed neutrinos. We outline the rich and constrained neutrino phenomenology that results from this proposal.

Theories of darkenergy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.

Full Text Available We present phase shift measurements for neutron matter waves in vacuum and in low pressure Helium using a method originally developed for neutron scattering length measurements in neutron interferometry. We search for phase shifts associated with a coupling to scalar fields. We set stringent limits for a scalar chameleon field, a prominent quintessence darkenergy candidate. We find that the coupling constant β is less than 1.9×107 for n=1 at 95% confidence level, where n is an input parameter of the self-interaction of the chameleon field φ inversely proportional to φn.

These lecture notes review the theoretical problems associated with coarse-graining the observed inhomogeneous structure of the universe at late epochs, of describing average cosmic evolution in the presence of growing inhomogeneity, and of relating average quantities to physical observables. In particular, a detailed discussion of the timescape scenario is presented. In this scenario, darkenergy is realized as a misidentification of gravitational energy gradients which result from gradients in the kinetic energy of expansion of space, in the presence of density and spatial curvature gradients that grow large with the growth of structure. The phenomenology and observational tests of the timescape model are discussed in detail, with updated constraints from Planck satellite data. In addition, recent results on the variation of the Hubble expansion on < 100/h Mpc scales are discussed. The spherically averaged Hubble law is significantly more uniform in the rest frame of the Local Group of galaxies than in t...

In Verlinde's entropic force scenario of gravity, Newton's laws and Einstein equations can be obtained from the first principles and general assumptions. However, the equipartition law of energy is invalid at very low temperatures.We show clearly that the threshold of the equipartition law of energy is related with horizon of the universe. Thus, a one-dimensional Debye (ODD) model in the direction of radius of the modified entropic force (MEF) may be suitable in description of the accelerated expanding universe. We present a Friedmann cosmic dynamical model in the ODD-MEF framework. We examine carefully constraints on the ODD-MEF model from the Union2 compilation of the Supernova Cosmology Project (SCP) collaboration, the data from the observation of the large-scale structure (LSS) and the cosmic microwave background (CMB), i.e. SNe Ia+LSS+CMB. The combined numerical analysis gives the best-fit value of the model parameters ζ(≈) 10-9 and Ωm0 = 0.224, with x2min=591.156. The corresponding age of the universe agrees with the result of D. Spergel et al. [J.M. Bardeen, B. Carter, and S.W. Hawking, Commun. Math. Phys. 31 (1973) 161] at 95% confidence level. The numerical result also yields an accelerated expanding universe without invoking any kind of darkenergy. Taking ζ(≡ 2πωD/H0) as a running parameter associated with the structure scale r, we obtain a possible unified scenario of the asymptotic flatness of the radial velocity dispersion of spiral galaxies, the accelerated expanding universe and the Pioneer 10/11 anomaly in the entropic force framework of Verlinde.

We study physics of clusters of galaxies embedded in the cosmic darkenergy background. Under the assumption that darkenergy is described by the cosmological constant, we show that the dynamical effects of darkenergy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by darkenergy: (1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the darkenergy antigravity; (2) the halo averaged density is equal to two densities of darkenergy; (3) the halo edge (cut-off) density is the darkenergy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by darkenergy: the maximum of the potential is located at the zero-gravity radius of the cluster.

We study physics of clusters of galaxies embedded in the cosmic darkenergy background. Under the assumption that darkenergy is described by the cosmological constant, we show that the dynamical effects of darkenergy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by darkenergy: 1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the darkenergy antigravity; 2) the halo averaged density is equal to two densities of darkenergy; 3) the halo edge (cut-off) density is the darkenergy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by darkenergy: the maximum of the potential is located at the zero-gravity radius of the cluster.

We review the parametrized post-Friedmann (PPF) method within the framework of interacting darkenergy model for a FRW background. We assess the possibility of using such treatment for curing a "bad" interaction from its large-scale instabilities, usually presented within the standard linear perturbation theory. Regarding the Markov Chain Monte-Carlo analysis, our global fitting combines several cosmological probes including the cosmic microwave background (WMAP9+Planck) data, barion acoustic oscillation (BAO) measurements, JLA sample of supernovae, Hubble constant (HST), and redshift-space distorsion (RSD) measurements through the ${\\rm f}\\sigma_{8}{\\rm (z)}$ data points. The joint observational analysis of ${\\rm Planck+WP+JLA+BAO+HST+RSD}$ data leads to a coupling parameter, $\\xi_{c}=0.00140_{-0.00080}^{+0.00079}$ at $1\\sigma$ level for vanishing momentum transfer potential, whereas the aforesaid value is reduced in a $0.022\\%$ when the momentum transfer potential is switched on. The CMB power spectrum show...

In the context of $f(\\mathcal{R})$ gravity, darkenergy is a geometrical fluid with negative equation of state. Since the function $f(\\mathcal{R})$ is not known \\emph{a priori}, the need of a model independent reconstruction of its shape represents a relevant technique to determine which $f(\\mathcal{R})$ model is really favored with respect to others. To this aim, we relate cosmography to a generic $f(\\mathcal R)$ and its derivatives in order to provide a model independent investigation at redshift $z \\sim 0$. Our analysis is based on the use of three different cosmological distance definitions, in order to alleviate the duality problem, i.e. the problem of which cosmological distance to use with specific cosmic data sets. We therefore consider the luminosity, $d_L$, flux, $d_F$, and angular, $d_A$, distances and we find numerical constraints by the Union 2.1 supernovae compilation and measurement of baryonic acoustic oscillations, at $z_{BAO}=0.35$. We notice that all distances reduce to the same expression,...

In this work we use cosmography to alleviate the degeneracy among cosmological models, proposing a way to parameterize matter and darkenergy in terms of cosmokinematics quantities. The recipe of using cosmography allows to expand observable quantities in Taylor series and to directly compare those expansions with data. We adopt this strategy and we propose a fully self-consistent parametrization of the total energy density driving the late time universe speed up. Afterwards, we describe a feasible \\emph{cosmographic darkenergy model}, in which matter is fixed whereas darkenergy evolves by means of the cosmographic series. Our technique provides robust constraints on cosmokinematic parameters, permitting one to separately bound matter from darkenergy densities. Our cosmographic darkenergy model turns out to be one parameter only, but differently from the $\\Lambda$CDM paradigm, it does not contain ansatz on the darkenergy form. In addition, we even determine the free parameter of our model in suitable $1\\...

We analyse the late time cosmology and the gravitational properties of doubly coupled bigravity in the vielbein formalism when the mass of the massive graviton is of the order of the present Hubble rate. We focus on one of the two branches of background cosmology where the ratio between the scale factors of the two metrics is algebraically determined. The Universe evolves from a matter dominated epoch to a darkenergy dominated era where the equation of state of darkenergy can always be made close to -1 now by appropriately tuning the graviton mass. We also analyse the perturbative spectrum of the theory in the quasi static approximation well below the strong coupling scale where no instability is present and we show that there are five scalar degrees of freedom, two vectors and two gravitons. In a cosmological FRW background for both metrics, four of the five scalars are Newtonian potentials which lead to a modification of gravity on large scales. In this scalar sector, gravity is modified with effects on b...

Galileon models are among the most appealing candidates for DarkEnergy. The reason is twofold: classically, they provide a tracking solution leading to an almost DeSitter space starting from very generic initial conditions in the deep radiation era. The second reason is the standard lore that Galileons are quantum mechanically stable. The latter property is certainly true in flat space-time, thanks to the non-renormalization theorems of galilean coupling constants. However, in a cosmological background, we show that quantum effects might dominate the classical trajectory. Assuming the radiation era to last at least up to the electroweak phase transition, the trajectory with initial conditions sitting on the tracker is ruled out. On the other hand, it is always possible to find a sub-space of initial conditions such that the darkenergy solution approaches stably the tracker at late times. Fixing the value of initial conditions that best fit current data, and assuming that the galileon effective theory is val...

We present a Bayesian approach to combine $Planck$ data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters ($0.056 3$ keV) observed with $Chandra$. We exploited the high-level of similarity of the emission measure in the cluster outskirts as cosmology proxy. The cosmological parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependency of the gas fraction. This cosmological test, in combination with $Planck$+SNIa data, allows us to put a tight constraint on the darkenergy models. For a constant-$w$ model, we have $w=-1.010\\pm0.030$ and $\\Omega_m=0.311\\pm0.014$, while for a time-evolving equation of state of darkenergy $w(z)$ we have $\\Omega_m=0.308\\pm 0.017$, $w_0=-0.993\\pm0.046$ and $w_a=-0.123\\pm0.400$. Constraints on the cosmology are further improved by adding priors on the gas f...

Inspired by the multiverse scenario, we study a heterotic darkenergy model in which there are two parts, the first being the cosmological constant and the second being the holographic darkenergy, thus this model is named the $\\Lambda$HDE model. By studying the $\\Lambda$HDE model theoretically, we find that the parameters $c$ and $\\Omega_{hde}$ are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the $\\Lambda$HDE model by using the recent observational data. We find the model yields $\\chi^2_{\\rm min}=426.27$ when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant $\\Lambda$CDM model (431.35). At 68.3\\% CL, we obtain $-0.07

Darkenergy (DE) is not necessarily uniform when other sources of gravity are present: interaction with matter leads to its variation in space and time. We study cosmological implications of this fact by analyzing cosmological models in which DE density interacts with matter and thus changes with time. We model the DE--matter interaction by specifying the rate of change of the DE density as an arbitrary function of it and the density of matter, in a single--phase case. In the case of several matter components interacting with darkenergy we assume the rate of every interacting phase density to be an arbitrary function of this density and the DE density. We describe some properties of cosmological solutions valid for a general law of DE--matter interaction, and discuss physical admissibility of the interaction laws. We study numerous families of exact solutions, both singular, non-singular, and mixed. Some of them exhibit interesting properties, such as, for instance, absence of the horizon problem due to the ...

We present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056 z z) we have Ωm = 0.308 ± 0.017, w0 = -0.993 ± 0.046 and wa = -0.123 ± 0.400. Constraints on the cosmology are further improved by adding priors on the gas fraction evolution from hydrodynamic simulations. Current data favour the cosmological constant with w ≡ -1, with no evidence for dynamic darkenergy. We checked that our method is robust towards different sources of systematics, including background modelling, outlier measurements, selection effects, inhomogeneities of the gas distribution and cosmic filaments. We also provided for the first time constraints on which definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmological test has the capacity to provide a generational leap forward in our understanding of the equation of state of darkenergy.

A Friedman cosmology is investigated based on scalar-tensor gravitation with general metric coupling and scalar potential functions. We show that for a broad class of such functions, the scalar field can be dynamically trapped using a recently suggested mechanism. The trapped scalar can drive inflation and accelerated cosmic expansion, compatible with standard requirements. The inflationary phase admits a natural exit with a value of the Hubble parameter dictated by the duration of inflation in a parameter independent manner. For inflationary duration consistent with the GUT description, the resulting Hubble parameter is found to be consistent with its observed value. - Highlights: • First model for inflation and darkenergy in cosmology and core-collapse supernovae in astronomy to be unified under the same theory. • Achieved with a natural simple extension of Einstein's General Relativity using a new scalar field. • Potentially far-researching consequences in cosmology for dark matter, darkenergy and inflation, testable through core-collapse supernovae.

We consider the angular power spectrum in a finite universe with different boundary conditions and perform a fit to the CMB, LSS and supernova data. A finite universe could be the consequence of a holographic constraint, giving rise to an effective IR cutoff at the future event horizon. In such a model there is a cosmic duality relating the darkenergy equation of state and the power spectrum, which shows a suppression and oscillatory behaviour that is found to describe the low l features extremely well. However, much of the discussion here will also apply if we actually live inside an expanding bubble that describes our universe. The best fit to the CMB and LSS data turns out to be better than in the standard Lambda-CDM model, but when combined with the supernova data, the holographic model becomes disfavored. We speculate on the possible implications.

A dynamical system analysis related to Dirac Born Infeld (DBI) cosmological model has been investigated in this present work. For spatially flat FRW space time, the Einstein field equation for DBI scenario has been used to study the dynamics of DBI darkenergy interacting with dark matter. The DBI darkenergy model is considered as a scalar field with a nonstandard kinetic energy term. An interaction between the DBI darkenergy and dark matter is considered through a phenomenological interaction between DBI scalar field and the dark matter fluid. The field equations are reduced to an autonomous dynamical system by a suitable redefinition of the basic variables. The potential of the DBI scalar field is assumed to be exponential. Finally, critical points are determined, their nature have been analyzed and corresponding cosmological scenario has been discussed.

We study cosmological dynamics of an extended gravitational theory that gravity is coupled non-minimally with derivatives of a darkenergy component and there is also a phenomenological interaction between the darkenergy and dark matter. Depending on the direction of energy flow between the dark sectors, the phenomenological interaction gets two different signs. We show that this feature affects the existence of attractor solution, the rate of growth of perturbations and stability of the solutions. By considering an exponential potential as a self-interaction potential of the scalar field, we obtain accelerated scaling solutions that are attractors and have the potential to alleviate the coincidence problem. While in the absence of the nonminimal derivative coupling there is no attractor solution for phantom field when energy transfers from dark matter to darkenergy, we show an attractor solution exists if one considers an explicit nonminimal derivative coupling for phantom field in this case of energy tran...

We show the way of dark matter and darkenergy presentation via ansatzs on the kinetic energies of the fields in the two-component chiral cosmological model. To connect a kinetic interaction of dark matter and darkenergy with observational data the reconstruction procedure for the chiral metric component $h_{22}$ and the potential of (self)interaction $V$ has been developed. The reconstruction of $h_{22}$ and $V$ for the early and later inflation have been performed. The proposed model is confronted to $\\Lambda CDM$ model as well.

A cosmological model of an holographic darkenergy interacting with dark matter throughout a decaying term of the form Q=3({lambda}{sub 1}{rho}{sub DE}+{lambda}{sub 2}{rho}{sub m})H is investigated. General constraint on the parameters of the model are found when accelerated expansion is imposed and we found a phantom scenario, without any reference to a specific equation of state for the darkenergy. The behavior of equation of state for darkenergy is also discussed.

In this paper, we consider a simple brane model with a generic darkenergy component which could drive the accelerated expansion at late times of the Universe. We use the Supernovae type Ia, $H(z)$, baryon acoustic oscillations, and cosmic microwave background radiation measurements to constrain the brane tension, which is the main observable of the theory. From the study, we found an important tension between the different data sets and evidence of no gravity modifications by the existence of an extra dimension. Although this specific braneworld model is not compatible with the current cosmological observations and offers no new insights into the darkenergy problem, it is not ruled out either. Our results show the need to further test of the braneworld model with appropriate correction terms.

@@ We consider a generalized quintom (GQ) darkenergy modelfor changing the equal weight of the negative-kinetic scalar field (phantom) and the normal scalar field (quintessence) in quintom darkenergy. Though the phantomdominated scaling solution is a stable late-time attractor, the early evolution of GQ is different from that of the quintom model and the adjustability of the darkenergy state equation in the model is improved.

@@ We study the constraints on the darkenergy model with constant equation of state parameter w = p/p and the holographic darkenergy model by using the weak gravity conjecture. The combination of weak gravity conjecture and the observational data gives w < -0.7 at the 3σ confidence level. The holographic darkenergy model realized by a scalar field is in swampland.

In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation of state of darkenergy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of darkenergy different from minus one, does not rule out vacuum...... with a Planck scale cutoff, the darkenergy effective equation of state is -0.96....

We investigate the model of holographic darkenergy with logarithmic correction to its energy density. This modification is motivated from the loop quantum gravity corrections to the entropy-area law. We also consider an interaction between darkenergy and dark matter. The behavior of the Hubble parameter (specially in the late time) is studied. Besides, conditions under which an accelerated universe can decelerate and also successive acceleration-deceleration phases can be occurred in the evolution of the universe is investigated.

This book presents a high-level study of cosmology with interacting darkenergy and no additional fields. It is known that darkenergy is not necessarily uniform when other sources of gravity are present: interaction with matter leads to its variation in space and time. The present text studies the cosmological implications of this circumstance by analyzing cosmological models in which the darkenergy density interacts with matter and thus changes with the time. The book also includes a translation of a seminal article about the remarkable life and work of E.B. Gliner, the first person to suggest the concept of darkenergy in 1965.

Here we generalize ideas of unified dark matter-darkenergy in the context of two measure theories and of dynamical space time theories. In two measure theories one uses metric independent volume elements and this allows one to construct unified dark matter-darkenergy, where the cosmological constant appears as an integration constant associated with the equation of motion of the measure fields. The dynamical space-time theories generalize the two measure theories by introducing a vector field whose equation of motion guarantees the conservation of a certain Energy Momentum tensor, which may be related, but in general is not the same as the gravitational Energy Momentum tensor. We propose two formulations of this idea: (I) by demanding that this vector field be the gradient of a scalar, (II) by considering the dynamical space field appearing in another part of the action. Then the dynamical space time theory becomes a theory of Diffusive Unified darkenergy and dark matter. These generalizations produce non-conserved energy momentum tensors instead of conserved energy momentum tensors which leads at the end to a formulation of interacting DE-DM dust models in the form of a diffusive type interacting Unified darkenergy and dark matter scenario. We solved analytically the theories for perturbative solution and asymptotic solution, and we show that the Λ CDM is a fixed point of these theories at large times. Also a preliminary argument as regards the good behavior of the theory at the quantum level is proposed for both theories.

By using a linearized non-vacuum late time solution in Brans-Dicke cosmology we account for the seventy five percent darkenergy contribution but not for approximately twenty-three percent dark matter contribution to the present day energy density of the universe.

In this work we present a model of the universe in which darkenergy is modelled explicitely with both a dynamical quintessence field and a cosmological constant. Our results confirm the possibility of a collapsing universe (for a given region of the parameter space), which is necessary for an adequate definition of string theory. We have also reproduced the measurements of modulus distance from supernovae with good accuracy.

In this work we present a model of the universe in which darkenergy is modeled explicitly with both a dynamical quintessence field and a cosmological constant. Our results confirm the possibility of a future collapsing universe (for a given region of the parameter space), which is necessary for a consistent formulation of both string and quantum field theories. The predictions of this model for distance modulus of supernovae are similar to those of the standard ΛCDM model.

Below scales of about 100/h Mpc our universe displays a complex inhomogeneous structure dominated by voids, with clusters of galaxies in sheets and filaments. The coincidence that cosmic expansion appears to start accelerating at the epoch when such structures form has prompted a number of researchers to question whether darkenergy is a signature of a failure of the standard cosmology to properly account, on average, for the distribution of matter we observe. Here I discuss the timescape scenario, in which cosmic acceleration is understood as an apparent effect, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the nonlinear growth of cosmic structure. I discuss conceptual issues related to the averaging problem, and their impact on the calibration of local geometry to the solutions of the volume-average evolution equations corrected by backreaction, and the question of nonbaryonic dark matter in the timescape framework. I further discuss recent work on ...

The goal of this program was to design, build, test, and characterize a flight qualified calibration source and monitor for a DarkEnergy related experiment: ACCESS - 'Absolute Color Calibration Experiment for Standard Stars'. This calibration source, the On-board Calibration Monitor (OCM), is a key component of our ACCESS spectrophotometric calibration program. The OCM will be flown as part of the ACCESS sub-orbital rocket payload in addition to monitoring instrument sensitivity on the ground. The objective of the OCM is to minimize systematic errors associated with any potential changes in the ACCESS instrument sensitivity. Importantly, the OCM will be used to monitor instrument sensitivity immediately after astronomical observations while the instrument payload is parachuting to the ground. Through monitoring, we can detect, track, characterize, and thus correct for any changes in instrument senstivity over the proposed 5-year duration of the assembled and calibrated instrument.

The DarkEnergy Camera (DECam) has been installed on the V. M. Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. This major upgrade to the facility has required numerous modifications to the telescope and improvements in observatory infrastructure. The telescope prime focus assembly has been entirely replaced, and the f/8 secondary change procedure radically changed. The heavier instrument means that telescope balance has been significantly modified. The telescope control system has been upgraded. NOAO has established a data transport system to efficiently move DECam's output to the NCSA for processing. The observatory has integrated the DECam highpressure, two-phase cryogenic cooling system into its operations and converted the Coudé room into an environmentally-controlled instrument handling facility incorporating a high quality cleanroom. New procedures to ensure the safety of personnel and equipment have been introduced.

This thesis considers several models that connect different areas of particle physics and cosmology. Our first discussion in this context concerns a baryogenesis scenario, in which the baryon asymmetry of our universe is created through the dynamics of a darkenergy field, thereby illustrating that these two topics might be related. Subsequently, several neutrino mass models are analyzed, which make use of an extra-dimensional setting to overcome certain problems of their fourdimensional counterparts. The central discussion of this thesis concerns a leptogenesis model with many standard model singlets. Amongst other things, we show that the presence of these states can lower the standard bound for the necessary reheating temperature of the universe by at least one and a half orders of magnitude. To further motivate this approach, we also discuss an explicit, extradimensional leptogenesis scenario that naturally yields many of the ingredients required in this context. (orig.)

In the search for an explanation for the current acceleration of the Universe, scalar fields are the most simple and useful tools to build models of darkenergy. This field, however, must in principle couple with the rest of the world and not necessarily in the same way to different particles or fluids. We provide the most complete dynamical system analysis to date, consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. We perform a detailed study of the existence and stability conditions of the systems and comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given current limits on the variation of the fine-structure constant.

In the search for an explanation for the current acceleration of the Universe, scalar fields are the most simple and useful tools to build models of darkenergy. This field, however, must in principle couple with the rest of the world and not necessarily in the same way to different particles or fluids. We provide the most complete dynamical system analysis to date, consisting of a canonical scalar field conformally and disformally coupled to both dust and radiation. We perform a detailed study of the existence and stability conditions of the systems and comment on constraints imposed on the disformal coupling from Big-Bang Nucleosynthesis and given current limits on the variation of the fine-structure constant.

We propose a minimal description of single field darkenergy/modified gravity within the effective field theory formalism for cosmological perturbations, which encompasses most existing models. We start from a generic Lagrangian given as an arbitrary function of the lapse and of the extrinsic and intrinsic curvature tensors of the time hypersurfaces in unitary gauge, i.e. choosing as time slicing the uniform scalar field hypersurfaces. Focusing on linear perturbations, we identify seven Lagrangian operators that lead to equations of motion containing at most two (space or time) derivatives, the time-dependent coefficients of three of these operators being determined only by the background evolution. We then establish a dictionary that translates any existing or future model whose Lagrangian can be written in the above form into our parametrized framework. As an illustration, we show that Horndeski's-or generalized Galileon-theories can be described, up to linear order, by only six of the seven operators menti...

We propose a universal description of darkenergy and modified gravity that includes all single-field models. By extending a formalism previously applied to inflation, we consider the metric universally coupled to matter fields and we write in terms of it the most general unitary gauge action consistent with the residual unbroken symmetries of spatial diffeomorphisms. Our action is particularly suited for cosmological perturbation theory: the background evolution depends on only three operators. All other operators start at least at quadratic order in the perturbations and their effects can be studied independently and systematically. In particular, we focus on the properties of a few operators which appear in non-minimally coupled scalar-tensor gravity and galileon theories. In this context, we study the mixing between gravity and the scalar degree of freedom. We assess the quantum and classical stability, derive the speed of sound of fluctuations and the renormalization of the Newton constant. The scalar ca...

I will present the current status of weak lensing results from the DarkEnergy Survey (DES). DES will survey 5000 square degrees in five photometric bands (grizY), and has already provided a competitive weak lensing catalog from Science Verification data covering just 3% of the final survey footprint. I will summarize the status of shear catalog production using observations from the first year of the survey and discuss recent weak lensing science results from DES. Finally, I will report on the outlook for future cosmological analyses in DES including the two-point cosmic shear correlation function and discuss challenges that DES and future surveys will face in achieving a control of systematics that allows us to take full advantage of the available statistical power of our shear catalogs.

We reconsider the entropic-force model in which both kind of Hubble terms ${\\dot H}$ and $H^{2}$ appear in the effective darkenergy (DE) density affecting the evolution of the main cosmological functions, namely the scale factor, deceleration parameter, matter density and growth of linear matter perturbations. However, we find that the entropic-force model is not viable at the background and perturbation levels due to the fact that the entropic formulation does not add a constant term in the Friedmann equations. On the other hand, if on mere phenomenological grounds we replace the ${\\dot H}$ dependence of the effective DE density with a linear term $H$ without including a constant additive term, we find that the transition from deceleration to acceleration becomes possible but the recent structure formation data \

We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure darkenergy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.

Nucleon self-energies and interaction potentials in supernova (SN) matter, which are known to have an important effect on nucleosynthesis conditions in SN ejecta are investigated. Corresponding weak charged-current interaction rates with unbound nucleons that are consistent with existing SN equations of state (EOSs) are specified. The nucleon self-energies are made available online as electronic tables. The discussion is mostly restricted to relativistic mean-field models. In the first part of the article, the generic properties of this class of models at finite temperature and asymmetry are studied. It is found that the quadratic expansion of the EOS in terms of asymmetry works reasonably well at finite temperatures and deviations originate mostly from the kinetic part. The interaction part of the symmetry energy is found to be almost temperature independent. At low densities, the account of realistic nucleon masses requires the introduction of a linear term in the expansion. Finally, it is shown that the important neutron-to-proton potential difference is given approximately by the asymmetry of the system and the interaction part of the zero-temperature symmetry energy. The results of different interactions are then compared with constraints from nuclear experiments and thereby the possible range of the potential difference is limited. In the second part, for a certain class of SN EOS models, the formation of nuclei is considered. Only moderate modifications are found for the self-energies of unbound nucleons that enter the weak charged-current interaction rates. This is because in the present approach the binding energies of bound states do not contribute to the single-particle energies of unbound nucleons.

It was argued that the vacuum energy of the Veneziano ghost field of QCD, in a time-dependent background, can be written in the general form, $H + O(H^2)$, where $H$ is the Hubble parameter. Based on this, a phenomenological darkenergy model whose energy density is of the form $\\rho=\\alpha H+\\beta H^{2}$ was recently proposed to explain the darkenergy dominated universe. In this paper, we investigate this generalized ghost darkenergy model in the setup of Brans-Dicke cosmology. We study the cosmological implications of this model. In particular, we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of this darkenergy model. It is shown that the equation of state parameter of the new ghost darkenergy can cross the phantom line ($w_D=-1$) provided the parameters of the model are chosen suitably.

In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation of state of darkenergy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of darkenergy different from minus one, does not rule out vacuum energy as darkenergy. It also indicates an interesting possibility that precise measurements of the infrared properties of darkenergy can be used to probe the ultraviolet cutoff scale of effective quantum field theory coupled to gravity. In a toy model with a vacuum energy dominated universe with a Planck scale cutoff, the darkenergy effective equation of state is -0.96.

Using a new method called the statefinder diagnostics which can make one darkenergy model differ from the others, we investigate the dynamics of Born-Infeld (B-I) type darkenergy model. The evolution trajectory of B-I type darkenergy with Mexican hat potential model with respect to e-folding time N is shown in the r (s) diagram, When the parameter of noncanonical kinetic energy term η→0 or kinetic energy ψ2→0, the B-I type darkenergy (K-essence) model reduces to the quintessence model or the ACDM model corresponding to the statefinder pair {r, s}={1, 0} respectively. As a result, the evolution trajectory of our model in the r (s) diagram in Mexican hat potential is quite different from those of other darkenergy models. The current values of parameters Ω,ψ and ω,ψ in this model meet the latest observations WMAP5 well.

We consider the possibility of an interaction in the dark sector in the presence of massive neutrinos, and investigate the observational constraints using the most recent CMB anisotropy data in combination with type Ia supernovae, baryon acoustic oscillations, and Hubble parameter measurements. We find that a coupled quintessence with massive neutrinos is mildly favored by the present observational data. The model with massive neutrinos is found to be a promising one to alleviate the current tension between local and global determinations of Hubble constant.

The existence of dark matter and darkenergy in cosmology is implied by various observations, however, they are still unclear because they have not been directly detected. In this Letter, an unified model of darkenergy and dark matter that can explain the evolution history of the Universe later than inflationary era, the time evolution of the growth rate function of the matter density contrast, the flat rotation curves of the spiral galaxies, and the gravitational experiments in the solar system is proposed in mimetic matter model.

The origin of the observed darkenergy could be explained entirely within the standard model, with no new fields required. We show how the low-energy sector of the chiral QCD Lagrangian, once embedded in a nontrivial spacetime, gives rise to a cosmological vacuum energy density which can be can be presented entirely in terms of QCD parameters and the Hubble constant $H$ as $\\rho_\\Lambda \\simeq H \\cdot m_q\\la\\bar{q}q\\ra /m_{\\eta'} \\sim (4.3\\cdot 10^{-3} \\text{eV})^4$. In this work we focus on the dynamics of the ghost fields that are essential ingredients of the aforementioned Lagrangian. In particular, we argue that the Veneziano ghost, being unphysical in the usual Minkowski QFT, becomes a physical degree of freedom if the universe is expanding. As an immediate consequence, all relevant effects are naturally very small as they are proportional to the rate of expansion $H/ \\Lqcd \\sim 10^{-41}$. The co-existence of these two drastically different scales ($\\Lqcd \\sim 100 $ MeV and $H \\sim 10^{-33}$ eV) does not...

The local measurement of $H_0$ is in tension with the prediction of $\\Lambda$CDM model based on the Planck data. This tension may imply that darkenergy is strengthened in the late-time Universe. We employ the latest cosmological observations on CMB, BAO, LSS, SNe, $H(z)$ and $H_0$ to constrain several interacting darkenergy models. Our results show no significant indications for the interaction between darkenergy and dark matter. The $H_0$ tension can be moderately alleviated, but not totally released.

A model for a flat homogeneous and isotropic Universe composed of darkenergy, dark matter, neutrinos, radiation and baryons is analyzed. The fields of dark matter and neutrinos are supposed to interact with the darkenergy. The darkenergy is considered to obey either the van der Waals or the Chaplygin equations of state. The ratio between the pressure and the energy density of the neutrinos varies with the red-shift simulating massive and non-relativistic neutrinos at small red-shifts and non-massive relativistic neutrinos at high red-shifts. The model can reproduce the expected red-shift behaviors of the deceleration parameter and of the density parameters of each constituent.

We investigate the evolution of the viscous darkenergy (DE) interacting with the dark matter (DM) in the Einstein cosmology model. By using the linearizing theory of the dynamical system, we find that, in our model,there exists a stable late time scaling solution which corresponds to the accelerating universe. We also find the unstable solution under some appropriate parameters. In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting darkenergy with the dark matter. However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting darkenergy cosmology model. That is to say, both the non-perfect fluid model and the interacting the darkenergy cosmic model can alleviate or soften the singularity of the universe.%@@ We investigate the evolution of the viscous darkenergy (DE) interacting with the dark matter (DM) in the Einstein cosmology model.By using the linearizing theory of the dynamical system, we find that, in our model, there exists a stable late time scaling solution which corresponds to the accelerating universe.We also find the unstable solution under some appropriate parameters.In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting darkenergy with the dark matter.However, if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting darkenergy cosmology model.That is to say, both the non-perfect fluid model and the interacting the darkenergy cosmic model can alleviate or soften the singularity of the universe.

The interacting darkenergy model could propose a effective way to avoid the coincidence problem. In this paper, darkenergy is taken as a fluid with a constant equation of state parameter $w_x$. In a general gauge, we could obtain two sets of different perturbation equations when the momentum transfer potential is vanished in the rest frame of dark matter or darkenergy. There are many kinds of interacting forms from the phenomenological considerations, here, we choose $Q=3H\\xi_x\\rho_x$ which owns the stable perturbations in most cases. Then, according to the Markov Chain Monte Carlo method, we constrain the model by currently available cosmic observations which include cosmic microwave background radiation, baryon acoustic oscillation, type Ia supernovae, and $f\\sigma_8(z)$ data points from redshift-space distortion. Jointing the geometry tests with the large scale structure information, the results show a tighter constraint on the interacting model than the case without $f\\sigma_8(z)$ data. We find the int...

We study the impacts of interaction between dark matter and darkenergy in the context of ghost darkenergy model. Using the dynamical system analysis, we obtain the fixed points of the system for different types of interactions while the universe is filled with radiation, matter (including dark matter and luminous matter) and darkenergy components. We consider the stability of the fixed points in details for different cases. In all cases there is an unstable matter dominated epoch and a stable late time darkenergy dominated phase. However, we find that adding the linear interaction, the evolution of ghost darkenergy model does not contain the radiation dominated epoch in the early times which is a necessary point in any cosmic model. This failure resolved when we add the non-linear interaction to the model. We also find an upper bound for the value of the coupling constant of the interaction between dark matter and darkenergy as b < 0.57 . This bound is necessary to have a decelerating and unstable ma...

In this paper, we show that in the framework of chaotic braneworld inflation, after preheating, the remaining oscillating inflaton field can play the role of dark matter with the observed level. Augmented by a non-zero effective cosmological constant $\\Lambda_4$ on the brane, triple unification of inflation, dark matter and darkenergy by a single field is realized. Our model perhaps is the simplest one in the market of theories to achieve triple unification.

Supernova remnants are believed to be the sources of galactic cosmic rays. Within this framework, diffusive shock acceleration must operate in these objects and accelerate protons all the way up to PeV energies. To do so, significant amplification of the magnetic field at the shock is required. The goal of this paper is to investigate the capability of supernova remnants to accelerate PeV protons. We present analytic estimates of the maximum energy of accelerated protons under various assumptions about the field amplification at supernova remnant shocks. We show that acceleration up to PeV energies is problematic in all the scenarios considered. This implies that either a different (more efficient) mechanism of field amplification operates at supernova remnant shocks, or that the sources of galactic cosmic rays in the PeV energy range should be searched somewhere else.

In this paper we propose a stationary solution of Einstein's field equations describing Reissner-Nordstrom black hole in darkenergy background. It is to be regarded as the Reissner-Nordstrom black hole is embedded into the darkenergy solution producing Reissner-Nordstrom-darkenergy black hole. We find that the space-time geometry of Reissner-Nordstrom-darkenergy solution is Petrov type $D$ in the classification of space-times. It is also shown that the embedded space-time possesses an energy-momentum tensor of the electromagnetic field interacting with the darkenergy having negative pressure. We find the energy-momentum tensor for darkenergy violates the the strong energy condition due to the negative pressure, whereas that of the electromagnetic field obeys the strong energy condition. It is shown that the time-like vector field for an observer in the Reissner-Nordstrom-darkenergy space is expanding, accelerating, shearing and non-rotating. We investigate the surface gravity of the horizons for the em...

Darkenergy is investigated from the perspective of quantum cosmology. It is found that, together with an appropriate normal ordering factor q, only when there is darkenergy can the cosmological wave function be normalized. This interesting observation may require further attention. (orig.)

The expansion of the Universe appears to be accelerating, and the mysterious antigravity agent of this acceleration has been called “darkenergy.” To measure the dynamics of darkenergy, baryon acoustic oscillations (BAO) can be used. Previous discussions of the BAO darkenergy test have focused on direct measurements of redshifts of as many as 109 individual galaxies, by observing the 21 cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three-dimensional intensity mapping. If our estimates gain acceptance they may be the starting point for a new class of darkenergy experiments dedicated to large angular scale mapping of the radio sky, shedding light on darkenergy.

One of the major challenges for modern supernova surveys is identifying the galaxy that hosted each explosion. Is there an accurate and efficient way to do this that avoids investing significant human resources?Why Identify Hosts?One problem in host galaxy identification. Here, the supernova lies between two galaxies but though the centroid of the galaxy on the right is closer in angular separation, this may be a distant background galaxy that is not actually near the supernova. [Gupta et al. 2016]Supernovae are a critical tool for making cosmological predictions that help us to understand our universe. But supernova cosmology relies on accurately identifying the properties of the supernovae including their redshifts. Since spectroscopic followup of supernova detections often isnt possible, we rely on observations of the supernova host galaxies to obtain redshifts.But how do we identify which galaxy hosted a supernova? This seems like a simple problem, but there are many complicating factors a seemingly nearby galaxy could be a distant background galaxy, for instance, or a supernovas host could be too faint to spot.The authors algorithm takes into account confusion, a measure of how likely the supernova is to be mismatched. In these illustrations of low (left) and high (right) confusion, the supernova is represented by a blue star, and the green circles represent possible host galaxies. [Gupta et al. 2016]Turning to AutomationBefore the era of large supernovae surveys, searching for host galaxies was done primarily by visual inspection. But current projects like the DarkEnergy Surveys Supernova Program is finding supernovae by the thousands, and the upcoming Large Synoptic Survey Telescope will likely discover hundreds of thousands. Visual inspection will not be possible in the face of this volume of data so an accurate and efficient automated method is clearly needed!To this end, a team of scientists led by Ravi Gupta (Argonne National Laboratory) has recently

We extend a previous work by Reischke et al. by studying the effects of tidal shear on clustering darkenergy models within the framework of the extended spherical collapse model and using the Zel'dovich approximation. As in previous works on clustering darkenergy, we assumed a vanishing effective sound speed describing the perturbations in darkenergy models. To be self-consistent, our treatment is valid only on linear scales since we do not intend to introduce any heuristic models. This approach makes the linear overdensity δc mass dependent and similarly to the case of smooth darkenergy, its effects are predominant at small masses and redshifts. Tidal shear has effects of the order of per cent or less, regardless of the model and preserves a well-known feature of clustering darkenergy: When darkenergy perturbations are included, the models resemble better the Lambda cold dark matter evolution of perturbations. We also showed that effects on the comoving number density of haloes are small and qualitatively and quantitatively in agreement with what were previously found for smooth darkenergy models.

We describe the difference imaging pipeline (DiffImg) used to detect transients in deep images from the DarkEnergy Survey Supernova program (DES-SN) in its first observing season from Aug 2013 through Feb 2014. DES-SN is a search for transients in which ten 3-deg^2 fields are repeatedly observed in the g,r,i,z passbands with a cadence of about 1 week. The observing strategy has been optimized to measure high-quality light curves and redshifts for thousands of Type Ia supernova (SN Ia) with the goal of measuring darkenergy parameters. The essential DiffImg functions are to align each search image to a deep reference image, do a pixel-by-pixel subtraction, and then examine the subtracted image for significant positive detections of point-source objects. The vast majority of detections are subtraction artifacts, but after selection requirements and image filtering with an automated scanning program, there are 130 detections per deg^2 per observation in each band, of which only 25% are artifacts. Of the 7500 tr...

A confluence of scientific, financial, and political factors imply that launching two simpler, more narrowly defined dark-energy/microlensing satellites will lead to faster, cheaper, better (and more secure) science than the present EUCLID and WFIRST designs. The two satellites, one led by ESA and the other by NASA, would be explicitly designed to perform complementary functions of a single, dual-satellite dark-energy/microlensing ``mission''. One would be a purely optical wide-field camera, with large format and small pixels, optimized for weak-lensing, which because of its simple design, could be launched by ESA on relatively short timescales. The second would be a purely infrared satellite with marginally-sampled or under-sampled pixels, launched by NASA. Because of budget constraints, this would be launched several years later. The two would complement one another in 3 darkenergy experiments (weak lensing, baryon oscillations, supernovae) and also in microlensing planet searches. Signed international agr...

Interacting DarkEnergy and Dark Matter is used to go beyond the standard cosmology. We base our arguments on Planck data and conclude that an interaction is compatible with the observations and can provide a strong argument towards consistency of different values of cosmological parameters.

Full Text Available We consider a quintessence model of darkenergy inspired by scalar-tensor theories of gravity where the scalar field is nonminimally coupled to gravity and dark matter. By considering exponential potential as self-interaction potential, the stability and existence of the critical points are discussed in details. With nonminimally coupled dark sector with gravity, we obtain scaling solutions to address the coincidence problem by considering complex velocity for dark matter. The statefinder diagnostic shows that the equation of state reaches ΛCDM model in the future.

We investigate the corresponding relation between f(R) gravity and holographic darkenergy. We introduce a type of energy density from f(R) that has the same role as holographic darkenergy. We obtain the differential equation that specifies the evolution of the introduced energy density parameter based on a varying gravitational constant. We discover the relation for the equation of state parameter for low redshifts that contains varying G correction.

A model of a three-dimensional quantum vacuum based on Planck energy density as a universal property of a granular space is suggested. The possibility to provide an unifying explanation of dark matter and darkenergy as phenomena linked with the fluctuations of the three-dimensional quantum vacuum is explored. The changes and fluctuations of the quantum vacuum energy density generate a curvature of space-time similar to the curvature produced by a "darkenergy" density. The formation of large scale structures in the universe associated to the flattening of the orbital speeds of the spiral galaxies can be explained in terms of primary fluctuations of the quantum vacuum energy density without attracting the idea of dark matter.

In this paper the cosmological evolution of a holographic darkenergy model with a non-linear interaction between the darkenergy and dark matter components in a FRW type flat universe is analysed. In this context, the deceleration parameter $q$ and the equation state $w_{\\Lambda}$ are obtained. We found that, as the square of the speed of sound remains positive, the model is stable under perturbations since early times; it also shows that the evolution of the matter and darkenergy densities are of the same order for a long period of time, avoiding the so--called coincidence problem. We have also made the correspondence of the model with the darkenergy densities and pressures for the quintessence and tachyon fields. From this correspondence we have reconstructed the potential of scalar fields and their dynamics.

In the context of the induced matter theory of gravity, we investigate the possibility of deriving a 4D quintessential scenario where an interaction between darkenergy and dark matter is allowed, and the darkenergy component is modeled by a minimally coupled scalar field. Regarding the Ponce de Leon metric, we found that it is possible to obtain such scenario on which the energy densities of dark matter and darkenergy, are both depending of the fifth extra coordinate. We obtain that the 4D induced scalar potential for the quintessence scalar field, has the same algebraic form to the one found by Zimdahl and Pavon in the context of usual 4D cosmology.